Semiconductor storage device with volatile and nonvolatile memories to allocate blocks to a memory and release allocated blocks

ABSTRACT

A semiconductor storage device includes a first memory area configured in a volatile semiconductor memory, second and third memory areas configured in a nonvolatile semiconductor memory, and a controller which executes following processing. The controller executes a first processing for storing a plurality of data by the first unit in the first memory area, a second processing for storing data outputted from the first memory area by a first management unit in the second memory area, and a third processing for storing data outputted from the first memory area by a second management unit in the third memory area.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of and claims the benefitof priority from U.S. application Ser. No. 13/571,034, filed Aug. 9,2012, which is a divisional application of U.S. application Ser. No.13/271,838, filed Oct. 12, 2011, now abandoned, which is a continuationapplication of U.S. application Ser. No. 12/552,330, filed Sep. 2, 2009,now U.S. Pat. No. 8,065,470, which is a Continuation Application of PCTApplication No. PCT/JP2008/073950, filed Dec. 25, 2008, which waspublished under PCT Article 21(2) in English, and which is based uponand claims the benefit of priority from prior Japanese PatentApplications No. 2007-339943, filed Dec. 28, 2007; and No. 2008-046227,filed Feb. 27, 2008. The entire contents of each of the above areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor storage device with anonvolatile semiconductor memory.

2. Description of the Related Art

Like a NAND type flash memory, a nonvolatile semiconductor memory has atype which, when data is stored therein, once erases data in unitscalled a block and thereafter to perform writing, a type which performsreading and writing in units called a page, and a type in which a unitof erasing, reading, and writing is specified.

On the other hand, a unit, which is used when a host apparatus such as apersonal computer performs reading and writing of data from and to asecondary storage device such as a hard disk drive, is called a sector.The sector is determined independently from a unit of erasing, reading,and writing in the nonvolatile semiconductor memory.

For example, whereas a size of a block unit (a block size) in thenonvolatile semiconductor memory is 512 kB and a size of a page unit (apage size) is 4 kB, a size of a sector unit (a sector size) in the hostapparatus is 512 B.

In this way, in some cases, the unit of erasing, reading, and writing inthe nonvolatile semiconductor memory may be larger than the unit ofreading and writing in the host apparatus.

Therefore, when the secondary storage device such as a hard disk drivein a personal computer is comprised using the nonvolatile semiconductormemory, data of the sector size from the personal computer as the hostapparatus is required to be conformed to the block size and the pagesize of the nonvolatile semiconductor memory, and thus, to be writtentherein.

On the other hand, a flash memory, for example a NAND type flash memory,has characteristics in which the deterioration of memory cells isprogressed in accordance with the increasing of the erasing count of theblock, which is performed prior to writing of data. And therefore, aprocess called wear leveling is performed for uniformly distributingdata updating positions in the nonvolatile semiconductor memory so thaterasing counts of all memory cells in the nonvolatile semiconductormemory become substantially the same.

For example, a logical address of the secondary storage devicedesignated by the host apparatus is translated into a physical addressof a nonvolatile semiconductor memory representing the data updatingposition, whereby the data updating positions are uniformly distributed.

On the other hand, when the above address translation is performed in alarge-capacity secondary storage device, if the unit of data managementis a small size (for example, a page size), the correspondence list(address translation table or management table) between the logicaladdress and the physical address is enlarged. As a result, thecorrespondence list dose not fit in a main memory of a controller in thesecondary storage device, whereby there arises a problem that theaddress translation cannot be performed at high speed. Therefore, theunit of data management in the secondary storage device is required tohave a larger size than a page size, such as a block size.

In order to solve the above problem, there has been known a technique inwhich another block called a log block is provided so as to correspondto a block (data block) with data stored therein (see Jpn. Pat. ApplnKOKAI Publication No. 2002-366423, for example).

In the above technique, data is written in an empty page in the logblock, and when there is no empty page in the log block, or when thereis not enough log block area, the data stored in the log block isreflected to the data block to improve the writing efficiency.

However, the above technique has a problem that since the data block andthe log block have one-to-one correspondences, the number of blockscapable of being simultaneously updated is limited to the number of logblocks.

Namely, when the data of a small size is written in a large number ofblocks, the data reflection processing is performed in the state thatthere are a large number of empty pages in the log block, whereby thewriting efficiency is not improved.

In addition, in order to suppress the erasing count of the block, datais sometimes managed in units of the page size smaller than the blocksize, and the superseding data of the page size may be appended(additionally written) to another erased block.

In this case, since the superseding data of the page size is written inanother block, the old data originally stored becomes invalid data.However, when valid data exists in a block including the invalid data,data in the block cannot be erased for reuse.

This is because, the erasing is required to be performed in the blockunit, and therefore, when the valid data is stored in the same block,for the purpose of preventing erasing of the valid data, data in theblock cannot be erased until the valid data is rewritten in anotherblock.

The existence of the invalid data requires larger storage areas in thenonvolatile semiconductor memory than the amount of the valid data.

However, if the updating of the data progresses in the secondary storagedevice, the amount of the invalid data increases. And therefore, thedata capacity including the invalid data and the valid data becomeslarge. As a result, these data may not be able to be stored in thestorage area in the nonvolatile semiconductor memory.

For the purpose of deleting the invalid data, the process (compaction)in which the valid data collected from blocks is rewritten to an unusedblock is executed (see Jpn. Pat. Appln KOKAI Publication No.2005-222550, for example).

BRIEF SUMMARY OF THE INVENTION

A semiconductor storage device according to an aspect of the presentinvention comprises a first memory area configured in a volatilesemiconductor memory which performs writing of data by a first unit orless, the first unit being an access unit to the semiconductor storagedevice, second and third memory areas configured in a nonvolatilesemiconductor memory which performs writing of data by a second unit andperforms erasing of data by a third unit, the third unit being twice orlarger natural number times as large as the second unit, and acontroller executing; a first processing for storing a plurality of databy the first unit in the first memory area; a second processing forstoring data outputted from the first memory area by a first managementunit in the second memory area, the first management unit being twice orlarger natural number times as large as the first unit and being lessthan the third unit; and a third processing for storing data outputtedfrom the first memory area by a second management unit in the thirdmemory area, the second management unit being twice or larger naturalnumber times as large as the first management unit.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a diagram showing a first basic configuration;

FIG. 2 is a diagram showing a second basic configuration;

FIG. 3 is a diagram showing a cache management table;

FIG. 4 is a diagram showing a page management table;

FIG. 5 is a diagram showing a page management table;

FIG. 6 is a diagram showing a block management table;

FIG. 7 is a diagram showing a physical block management table;

FIG. 8 is a diagram showing a physical block management table;

FIG. 9 is a flowchart showing a data store process in a first memoryarea;

FIG. 10 is a flowchart showing a data output process from a first memoryarea;

FIG. 11 is a flowchart showing a data output process from a first memoryarea;

FIG. 12 is a diagram showing data transfer from the first memory area toa second memory area;

FIG. 13 is a diagram showing data transfer from the first memory area toa third memory area;

FIG. 14 is a diagram showing data transfer from the first memory area tothe third memory area;

FIG. 15 is flowchart showing data transfer from the second memory areato the third memory area;

FIG. 16 is a diagram showing a condition of the data transfer from thesecond memory area to the third memory area;

FIG. 17 is a diagram showing a system example;

FIG. 18 is a diagram showing a system example;

FIG. 19 is a diagram showing an example of compaction;

FIG. 20 is a diagram showing a configuration of a first embodiment;

FIG. 21 is a diagram showing a cache management table;

FIG. 22 is a diagram showing a page management table;

FIG. 23 is a diagram showing a block management table;

FIG. 24 is a diagram showing a page FIFO management table;

FIG. 25 is a diagram showing a physical block management table;

FIG. 26 is a flowchart showing a FIFO process in the fourth memory area;

FIG. 27 is a flowchart showing process P1;

FIG. 28 is a flowchart showing a process example 1 of compaction;

FIG. 29 is a flowchart showing a process example 2 of compaction;

FIG. 30 is a diagram showing a configuration of a second embodiment;

FIG. 31 is a diagram showing a track management table;

FIG. 32 is a diagram showing a track FIFO management table;

FIG. 33 is a diagram showing a physical block management table;

FIG. 34 is a flowchart showing a FIFO process in a fifth memory area;

FIG. 35 is a flowchart showing a process example 1 of compaction;

FIG. 36 is a flowchart showing a process example 2 of compaction;

FIG. 37 is a diagram showing a configuration of a third embodiment;

FIG. 38 is a flowchart showing a FIFO process in the fourth memory area;

FIG. 39 is a flowchart showing a process P1;

FIG. 40 is a diagram showing a state of the fourth memory area;

FIG. 41 is a flowchart showing a process example of a data transferprocess from the second memory area to the third memory area, and acompaction process;

FIG. 42 is a diagram showing a state of the second memory area;

FIG. 43 is a diagram showing a state of the second memory area;

FIG. 44 is a diagram showing a state of the second memory area;

FIG. 45 is a diagram showing a state of the second memory area;

FIG. 46 is a diagram showing a state of the second memory area;

FIG. 47 is a diagram for explaining an example of data management unit;

FIG. 48 is a diagram showing a cluster management table;

FIG. 49 is a flowchart showing a FIFO process in the fourth memory area;

FIG. 50 is a diagram showing an example of SSD;

FIG. 51 is a diagram showing a configuration example of one block;

FIG. 52 is a diagram showing threshold voltage distributions in a memorycell transistor;

FIG. 53 is a diagram showing a configuration example of a drive controlcircuit;

FIG. 54 is a diagram showing a configuration example of a processor;

FIG. 55 is a diagram showing an example of a portable computer; and

FIG. 56 is a diagram showing an example of a system of a portablecomputer.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the invention will be described withreference to the drawings.

I. Semiconductor Storage Device for Realizing the Improvement of WritingEfficiency 1. Outline

A semiconductor storage device according to this embodiment ischaracterized by storing sector unit data stream from a host apparatusin a first memory area, by distinguishing whether the data stored in thefirst memory area should be managed with a “small unit (first managementunit)” or a “large unit (second management unit)”, and by storing “smallunit” data and “large unit” data respectively in a second memory areaand a third memory area.

In addition, the semiconductor storage device according to thisembodiment is characterized by merging “small unit” data stored in thesecond memory area, into one “large unit” data, and storing the “largeunit” data in the third memory area.

A size of the “large unit” is a natural number times as large as a sizeof the “small unit”. In each “small unit” data, a plurality of sectorunit data is sequentially arranged in order of logical address.Similarly, in each “large unit” data, a plurality of sector unit data issequentially arranged in order of logical address.

In other words, the semiconductor storage device according to thisembodiment stores a plurality of sector unit data within a range ofnarrow logical address (fine grained data) by the “small unit” in thesecond memory area, and stores a plurality of sector data within a rangeof wide logical address (coarse grained data) by the “large unit” in thethird memory area.

Moreover, when a certain quantity of “small unit” data is accumulated inthe second memory area, the semiconductor storage device according tothis embodiment merges the data into “large unit” data and stores the“large unit” data in the third memory area (Defragmentation).

For example, the case where a size of the “small unit” is equal to asize of a page unit and a size of the “large unit” is equal to a size ofa block unit in a NAND-type flash memory can be considered. In otherwords, sector unit (a first unit) data is stored in the first memoryarea, page unit (a second unit) data is stored in the second memoryarea, and block unit (a third unit) data is stored in the third memoryarea.

In this case, sector unit data transferred from the host apparatus tothe semiconductor storage device is first stored in the first memoryarea. The data stored in the first memory area is determined whether itis transferred to the second memory area or to the third memory area, onthe basis of the number of data or the data amount.

Namely, when the data stored in the first memory area satisfies a firstcondition, the data is managed with the “large unit” and is stored ineach block of the third memory area as block unit data. In this case,the writing efficiency does not become lowered, even if block unit datais erased subsidiary to writing.

On the other hand, when the data stored in the first memory area failsto satisfy the first condition, the data is managed with the “smallunit” and is stored in each page of the second memory area as page unitdata. In this case, the erasing amount of block unit data can bedecreased by storing page unit data in appending manner.

The data of the “small unit” equivalent to the page unit stored in thesecond memory area is further selected based on a second condition. Aplurality of data including the selected data is merged into “largeunit” data. The “large unit” data is stored in each block of the thirdmemory area as block unit data.

The first condition is defined by the number of data, for example.

Namely, when the number of data stored in the first memory area reachesa predetermined threshold value, the data are transferred to the thirdmemory area, and when the number of data stored in the first memory areadoes not reach the predetermined threshold value, the data aretransferred to the second memory area.

Alternatively, it may be determined whether or not the total number ofthe data stored in the first and second memory areas reaches apredetermined threshold value. Namely, when the total number reaches thepredetermined threshold value, the data are transferred to the thirdmemory area, and when the total number dose not reach the predeterminedthreshold value, the data are transferred to the second memory area.

The second condition is defined by the writing order or the number ofthe valid data, for example.

When the second condition is defined by the writing order, the data in ablock with the earliest writing order detected from among the blocks inthe second memory area are sequentially selected, and the selected dataare transferred to the third memory area.

When the second condition is defined by the number of valid data, withrespect to each block in the second memory area, the number of validdata of the page unit stored in the second memory area is summed in alogical address range at the time when the logical address of valid datain a block is aligned by a size of the block unit, and the valid data ina block with the largest summed value are transferred to the thirdmemory area.

Incidentally, “the logical address is aligned by a predetermined size(such as a size of the page unit or the block unit)” means that thelogical address is rounded down to such an address that a reminder whenthe logical address is divided by the predetermined size is 0. Forexample, an address calculated by aligning the logical address A by thesize S is (A−(a remainder when A is divided by S)). Similarly, “thelogical address range aligned by a predetermined size” means that therange of the predetermined size from the address calculated by aligningthe logical address by the predetermined size.

The semiconductor storage device according to this embodiment canrealize the improvement of the writing efficiency, and the prevention ofthe performance deterioration and the life shortening, regardless thedata size or the data amount from a host apparatus.

Particularly, the effect of this embodiment is most obvious in the casein which the semiconductor storage device is comprised of a nonvolatilesemiconductor memory (for example, a NAND type flash memory) with aspecified unit of erasing, reading, and writing, and is used as asecondary storage device (SSD: Solid State Drive) for a personalcomputer.

The capacity of the above semiconductor storage device tends to becomelarger, and when the increasing of the capacity is realized by MLC(Multi Level Cell) technology in which plural bits are stored in onememory cell, the unit of erasing, reading, and writing tends to becomelarger, in order to keep a substantial write performance.

In addition, in a personal computer and the like, data on the secondarystorage device is often updated by the “small unit”. When this data ismanaged only with the “large unit” such as the block unit, the dataerasing amount against the data updating amount becomes larger, wherebythe writing efficiency is lowered, and the deterioration of the memorycell is accelerated.

As shown in this embodiment, the data stream from the host apparatus aredivided into the “small unit” and the “large unit”, and the “small unit”data and the “large unit” data are respectively written in the differentmemory areas, whereby the possibility of the occurrence of the aboveproblems can be reduced.

In other words, the data erasing amount of the nonvolatile semiconductormemory is optimized against data writing amount from the host apparatusand the writing efficiency is improved, by using two management units,the “small unit” and the “large unit”, in the semiconductor storagedevice.

2. Embodiment

An embodiment of the invention will be described.

The writing efficiency as a concept relating to this embodiment isdescribed.

With regard to the deterioration of memory cells in a flash memory, forexample a NAND type flash memory, the erasing amount of block unit datain the flash memory required for the writing data amount from the hostapparatus is an important factor.

In this embodiment, the data erasing amount is called a “value ofwriting efficiency”.

If the erasing amount of block unit data against the writing data amountis small, the value of writing efficiency becomes small, and theprogression of the deterioration of memory cells is relatively slowed.This phenomenon means that the writing efficiency is improved. On theother hand, if the erasing amount of block unit data is large, the valueof writing efficiency becomes large. This phenomenon means that thewriting efficiency is deteriorated.

Namely, in order to prevent the deterioration of memory cells in theflash memory, it is important to reduce the erasing amount of block unitdata, whereby to improve the writing efficiency.

There will be shown an example in which the writing efficiency in asemiconductor storage device using the flash memory is deteriorated.

In this example, a size of the block unit and a size of the page unit inthe flash memory are respectively assumed to be 512 kB and 4 kB, a sizeof the sector unit of a host apparatus is assumed to be 512 B, and asize of the data management unit is assumed to be 512 kB which is thesame as the block unit.

A process upon updating data Y, which has a size of 1 sector and haslogical address included in logical address range of data X, isconsidered in such a state that the data X with the same size as theblock unit is stored in the flash memory.

The data X is assumed to be stored in the entirety of a block B1 of theflash memory.

First, the data X from the block B1 is read out onto a temporary storingarea, and a part of the data X is superseded with the updating data Yfrom the host apparatus, whereby the latest data is created. Then, thedata in a block B2 different from the block B1 is erased, and the latestdata is written in the block B2.

In this process, as above mentioned, it is necessary to read the data Xof 512 kB from the block B1 in order to write the data Y of 512 Btherein, and further to erase the data of 512 kB in the block B2 inorder to write the latest data in the block B2.

Accordingly, the erasing amount in the flash memory is large withrespect to the writing data amount from the host apparatus, whereby thewriting efficiency is extremely bad.

The value of writing efficiency in this example is 512 kB/512 B=1024.

Usually, in the NAND type flash memory, it takes considerable time forblock erasing process and writing process, and therefore, thedeterioration of the writing efficiency means that the erasing amount ofblock unit data and the writing data amount in the erased block arelarge with respect to the writing data amount from the host apparatus,and, at the same time, means that the rate performance of thesemiconductor storage device is deteriorated.

(1) Basic Configuration

FIG. 1 shows a first basic configuration of the semiconductor storagedevice according to this embodiment.

A first memory area 11 temporarily stores data from a host apparatus.The data is written by a sector unit (a first unit) in the first memoryarea 11. The first memory area 11 is configured in a volatilesemiconductor memory such as a DRAM (Dynamic Random Access Memory), forexample.

The physical unit of reading/writing in a volatile semiconductor memorywhich comprises the first memory area 11 is the sector unit or less. Thehost apparatus executes an access to the semiconductor storage deviceusing a logical address with the sector unit (LBA: Logical BlockAddressing). Therefore, the first memory area 11 manages an input datawith the sector unit.

A second memory area is composed of blocks in a nonvolatilesemiconductor memory, for example, a NAND type flash memory. A thirdmemory area is composed of blocks in a nonvolatile semiconductor memory,for example, a NAND type flash memory.

The second and third memory areas 12 and 13 are respectively configuredin separate nonvolatile semiconductor memories (memory chips). Eachmemory chip may have different performance, such as writing performance,or may have different storage capacity. For example, the second memoryarea 12 may be configured in a NAND type flash memory with the SLC(Single level cell) technology, the third memory area 13 may beconfigured in a NAND type flash memory with the MLC (Multi level cell)technology.

The unit in which reading/writing is executed at one time is a page (asecond unit) and the unit in which erasing is executed at one time is ablock (a third unit), in the nonvolatile semiconductor memory. One blockunit is composed of a plurality of page units. In addition, thenonvolatile semiconductor memory according to this embodiment does notpermit to rewrite in the same page unless data in the block includingthe page is once erased.

Therefore, if superseding data (new data) is inputted from the hostapparatus, old data originally stored in the block, having the samelogical address as the new data, is treated as invalid data. The newdata is treated as valid data which has priority over the old data, andthe old data is treated as invalid data which is ignored by referring tothe new data.

To simplify the explanation, each of the units is assumed below:

A size of the “small unit (first management unit)” which is a datamanagement unit in the semiconductor storage device is equal to a sizeof the page unit (a storable data amount in one page). A size of the“large unit (second management unit)” is equal to a size of the blockunit (a storable data amount in one block). A size of the “small unit”is a natural number times as large as a size of the sector unit.

The first, second and third units representing a size of data do notinclude a redundant data (ECC: Error Checking/Correcting Code, internalcontrol flag, etc.) which is added in the semiconductor storage deviceto main data from the host apparatus.

In general, the system including the nonvolatile semiconductor memory,for example a NAND type flash memory, executes reading/writing in thestate of adding the redundancy data to the main data. But, forsimplifying the explanation, each of the units is assumed above.

The second memory area 12 stores data transferred from the first memoryarea 11 by the “small unit” which is equal to the page unit. The thirdmemory area 13 stores data transferred from the first memory area 11 orthe second memory area 12 by the “large unit” which is equal to theblock unit.

The second memory area 12 may have a capacity smaller than the capacityof the third memory area 13 because of controlling only part of dataupdated by “small unit”.

The following description, one block unit data is entirely stored in oneblock, and one page unit data is entirely stored in one page. Each blockis comprised of plural pages, and a plurality of page unit data isstored in one block.

A controller 10 has a CPU and a main memory, and can operate a programfor executing data management. In this embodiment, the functionsrealized by the controller 10 can be implemented as any of hardware andsoftware or the combination of the both. Whether these functions areimplemented as hardware or software depends on the practical embodimentor the design constraints imposed on the entire system. Those skilled inthe art can implement these functions by various methods for eachpractical embodiment, and the scope of the present invention includesdetermination of the implementation.

The controller 10 has, in the main memory, a cache management table, apage management table, a block management table, and a physical blockmanagement table, in order to manage where data accessed by the logicaladdress is stored in the first, second and third memory areas 11, 12,and 13.

When the main memory of the controller 10 is comprised of a volatilesemiconductor memory such as a DRAM, the first memory area 11 may beconfigured in the main memory of the controller 10.

FIG. 2 shows a second basic configuration of the semiconductor storagedevice according to this embodiment.

The second basic configuration is different in the following points fromthe first basic configuration of FIG. 1.

The second and third memory areas 12 and 13 are configured in anonvolatile semiconductor memory 22. The volatile semiconductor memorycomprising the first memory area 11 is assumed to be a DRAM, and thenonvolatile semiconductor memory 22 comprises the second and thirdmemory areas 12 and 13 is assumed to be a NAND type flash memory, forexample.

The second and third memory areas 12 and 13 are configured so as toshare a storage area in the nonvolatile semiconductor memory 22, and thecontroller 10 allocates blocks in the nonvolatile semiconductor memory22 to the second memory area 12 or the third memory area 13. Theallocation to the second and third memory areas 12, 13 is not static,but also dynamic. The allocation to the second and third memory areas12, 13 is controlled by the controller 10. The second and third memoryareas 12 and 13 may be configured over a plurality of nonvolatilesemiconductor memories (memory chips). The controller 10 may treatswhole plural blocks in nonvolatile semiconductor memories as oneabstracted storage region.

The controller 10 has, in the main memory, a cache management table, apage management table, a block management table, and a physical blockmanagement table.

In FIG. 1 and FIG. 2, these management tables are stored in anonvolatile semiconductor memory in the state of no power supply to thesemiconductor storage device. The controller 10 reads out thesemanagement tables onto the main memory in the time of the power supply.The controller 10 executes address translation in order to correlate thelogical address space designated from the host apparatus with thephysical position of the data in the nonvolatile semiconductor memory.

——Cache Management Table——

FIG. 3 shows an example of a cache management table.

The cache management table controls data stored in the first memory area11 of FIGS. 1 and 2 by the “small unit” which is equal to the page unit.The control of the valid data is executed by the sector unit.

It is assumed that one entry is assigned to one area of one page unit inthe first memory area 11.

The number of entries is assumed to be the number of page unit datawhich can be contained within the first memory area 11, that is, notlarger than (the total capacity of the first memory area 11)/(a size ofthe page unit).

A logical address of page unit data, a physical address of the firstmemory area 11, and a sector flag indicating the location of the validdata in the relevant area of the page unit are associated with eachentry.

The area of the page unit for temporarily storing data corresponded toeach entry is provided in the first memory area 11, and the physicaladdress of the area is stored in each entry. If the physical address ofthe area corresponding to the entry is specified, such as if the areasof the page unit are continuously disposed, the physical address is notrequired to be stored in the entry.

The each area of the page unit in the first memory area 11 is furtherdivided into areas of the sector unit in the cache management table. Adata status in each area of the sector unit is represented by settingthe value of the sector flag as “1” or “0”.

In an area with the sector flag of “1”, valid data from the hostapparatus is stored. In an area with the sector flag of “0”, the latestdata written from the host apparatus is not stored, whereby the area istreated as an invalid area. The entry in which all the sector flags are“0” is regarded to be an unused entry.

The configuration of the above cache management table is based on acontrol method called a full associative method in which the logicaladdress is assigned to each entry. However, the correspondence betweenthe logical address and the physical address in the first memory area 11may be controlled by an n-way set associative method or the like.

——Page Management Table——

FIG. 4 shows an example of a page management table.

The page management table controls data stored in the second memory area12 of FIGS. 1 and 2 by the “small unit” which is equal to the page unit.

It is assumed that one entry is assigned to one area of one page unit inthe second memory area 12.

The number of entries is assumed to be the number of page unit datawhich can be contained within the second memory area 12, that is, notlarger than (the total capacity of the second memory area 12)/(a size ofthe page unit).

A logical address of page unit data and a physical address of the secondmemory area 12 are associated with each entry.

For example, one page unit data with the physical address A is stored inthe first page of the block 0 in the second memory area 12 designated bythe physical address A, and one page unit data with the physical addressC is stored in the second page of the block 1 in the second memory area12 designated by the physical address C. An invalid entry isrepresented, for example, by means of providing a flag indicating thevalidity or invalidity of the entry, or storing an invalid logicaladdress or an invalid physical address in the entry.

FIG. 5 shows another example of a page management table. The pagemanagement table in FIG. 5 is explained later.

——Block Management Table——

FIG. 6 shows an example of a block management table.

The block management table controls data stored in the third memory area13 of FIGS. 1 and 2 by the “large unit” which is equal to the blockunit.

It is assumed that one entry is assigned to one area of one block unitin the third memory area 13.

The number of entries is assumed to be the number of block unit datawhich can be contained within the third memory area 13, that is, notlarger than (the total capacity of the third memory area 13)/(a size ofthe block unit).

Each entry is arranged in order of a logical address. A physical addresswhich corresponds to a logical address of the block unit data anddesignates a block in the third memory area 13 is associated with eachentry. The invalid entry is represented, for example, by means ofproviding a flag indicating the validity or invalidity of the entry, orstoring an invalid physical address in the entry.

——Physical Block Management Table——

FIGS. 7 and 8 show examples of a physical block management table.

The physical block management table of FIG. 7 is used in the first basicconfiguration and controls the usage (active/free) of blocks in thesecond and third memory areas 12 and 13 of FIG. 1. As shown in FIG. 7(a), a pointer to availability is stored in the physical block managementtable for the second memory area 12, and the physical block managementtable controls the availability of pages in a block.

As shown in FIG. 7( b), in order to save the storage area, theavailability of a page is not controlled by the physical blockmanagement table for the third memory area 13.

The physical block management table of FIG. 8 is used in the secondbasic configuration and controls whether the storage area (block) in thenonvolatile semiconductor memory 22 of FIG. 2 is used as the secondmemory area 12 (active), is used as the third memory area 13 (active),or is unused (free: no valid data exists therein). When the storage areais used as the second memory area 12, the physical block managementtable controls the availability of a page associated therewith.

It is assumed that one entry is assigned to one block (physical block)in the second and third memory areas 12, 13.

The number of entries is assumed to be not larger than the number ofblocks which can be used as a data area.

A physical address and the usage of a block designated by the physicaladdress are associated with each entry, and for the blocks used in thesecond memory area 12, the availability of pages are managed.

The page availability is configured to be able to distinguish“write-enable” state (this storage area is empty) from “write-inhibit”state (this storage area is invalid because old data has once writtentherein and new data is rewritten in another storage area) for eachpage.

In data writing sequence to each page, if a nonvolatile semiconductormemory can only perform writing of data in the ascending order of thephysical address, the page availability is managed by storing a positionof an empty page in which data can be appended in a block.

As the availability of pages in a block for the second memory area 12,the data structure shown in FIG. 4 that manages empty pages in a blockis adopted, for example.

In this embodiment, the page availability is stored in the physicalblock management table; however, as shown in FIG. 5, it may be stored inthe page management table. In this case, the page management table ispartitioned into units of a physical block used for the second memoryarea 12, and stores the logical address together with the pageavailability.

In the above description, for simplifying of the explanation, the “smallunit (first management unit)” used in the second memory area 12 isassumed to be the page unit, the “large unit (second management unit)”used in the third memory area 13 is assumed to be the block unit;however, the management units are not limited to this settings.

It is important that, in a nonvolatile semiconductor memory such as aNAND type flash memory, which comprises a secondary storage device as asubstitute for a hard disc drive (magnetic disk apparatus), the unit oferasing, reading, and writing, is specified.

For example, a page is controlled by being divided, specifically, a sizeof the “small unit” used in the second memory area 12 may be a naturalnumber times as large as a size of the sector unit and a size of thepage unit may be twice or larger natural number times as large as a sizeof the “small unit”.

Alternatively, plural pages are collectively controlled, specifically, asize of the “small unit” used in the second memory area 12 may be twiceor larger natural number times as large as a size of the page unit and asize of the block unit may be twice or larger natural number times aslarge as a size of the “small unit”.

Likewise, a block is controlled by being divided, specifically, a sizeof the “large unit” used in the third memory area 13 may be twice orlarger natural number times as large as a size of the “small unit” and asize of the block unit may be twice or larger natural number times aslarge as a size of the “large unit”.

Alternatively, plural blocks are collectively controlled, specifically,a size of the “large unit” used in the third memory area 13 may be twiceor larger natural number times as large as a size of the block unit.

The unit of erasing in the second and third memory areas 12 and 13 maybe the same (for example, the block size), or may be different bysimultaneously erasing plural blocks, and so on.

(2) Process Method

The process executed by the controller 10 of FIGS. 1 and 2 is described.

A. Data Store Process in the First Memory Area

The data store process in the first memory area 11 is described withreference to FIG. 9.

The input data from the host apparatus is first written in the firstmemory area 11 and the data is stored in the first memory area 11 for acertain period. At that time, the cache management table of FIG. 3 isupdated.

1. The controller 10 aligns the logical address of the input data by asize of the “small unit” which is equal to the page unit (Step ST 1).

2. The controller 10 searches the entry corresponding to the logicaladdress range aligned by a size of the page unit from the cachemanagement table (Step ST2).

3. The controller 10 judges whether there exists corresponding entry inthe first memory area 11. If the corresponding entry is detected in thefirst memory area 11, the controller 10 selects this entry and thisprocess goes to the step ST 8. If the corresponding entry is notdetected in the first memory area 11, this process goes to the step ST4.

4. The controller 10 searches the cache management table and judgeswhether there exists an unused entry (Step ST4). If the unused entry isdetected, this process goes to the step ST 6. If the unused entry is notdetected, this process goes to the step ST 5.

5. The controller 10 executes “data output process from the first memoryarea” which is described next. Whereby, the data is outputted from thefirst memory area 11 to the second memory area 12 and the third memoryarea 13 (Step ST5). As a result, the entry in the cache management tablecorresponding to the outputted data is set to be an unused entry. Atthat time, all sector flags in this entry are set to be “0”. Afterfinishing the settings, this process returns to the step ST4.

6. The controller 10 selects the unused entry for the input data fromthe host apparatus (Step ST6).

7. The controller 10 sets the logical address obtained by aligning thelogical address of the input data by a size of the page unit to theselected entry (Step ST7). Namely, the controller 10 determines theselected entry as the entry corresponding to the input data.

8. The controller 10 determines the physical address for data writingbased on the logical address of the input data and the logical addressand the physical address of the selected entry. The controller 10instructs the volatile semiconductor memory including the first memoryarea 11 to write the input data in the area designated by the physicaladdress (Step ST8).

In addition, the controller 10 sets the sector flags, corresponding tothe data written position in the area of the page unit, to be “1”.

In the case where the input data from the host apparatus is larger thanthe page size, plural entries in the cache management table may berequired. In such a case, the controller 10 updates the plural entriesby repeating the above process.

B. Data Output Process from the First Memory Area

The data output process from the first memory area 11 is described withreference to FIGS. 10 and 11.

The controller 10 selects page unit data which will be outputted fromthe first memory area 11 and transfers the data to the second memoryarea 12 or the third memory area 13 in accordance with a firstcondition. For example, the first condition is defined by the number ofdata. Specifically, the controller 10 executes following process (a) orprocess (b).

(a). The controller 10 counts the number of data in the first memoryarea 11 and determines to manage the data with either the “large unit”which is equal to the block unit or the “small unit” which is equal tothe page unit.

1. The controller 10 aligns a logical address LA of page unit (“smallunit”) data, which will be outputted, by a size of the block unit(“large unit”) (Step ST1).

2. The controller 10 counts up the number of entries included in thelogical address range of a size of the block unit by searching the cachemanagement table of FIG. 3 (Step ST2).

For example, according to the example of FIG. 12, the number of entriesincluded in the logical address range X aligned by a size of the blockunit is 3, that is, LA1, LA4, and LA6.

3. The controller 10 judges whether the number of entries is apredetermined threshold value or more. For example, the predeterminedthreshold value may be set to be 50% of the total number of page unit(“small unit”) data storable in one area of the block unit (“largeunit”) (Step ST3).

If the number of entries is less than the predetermined threshold value,the controller 10 transfers each data included in the logical addressrange to the second memory area 12 as data of the “small unit” which isequal to the page unit.

If the number of entries is not less than the predetermined thresholdvalue, the controller 10 transfers a plurality of data included in thelogical address range to the third memory area 13 as data of the “largeunit” which is equal to the block unit.

•“Small Unit” Case (See, the Flowchart of FIG. 10 and FIG. 12)

The controller 10 selects the data to be outputted from the first memoryarea 11 and transfers the selected data to the second memory area 12 asdata of the page unit. The steps on and after the step ST4 in FIG. 10are referred.

Hereinafter, a process in the case where one page unit data istransferred from the first memory area 11 is described. When plural pageunit data are transferred, the following process is repeated.

4. The controller 10 searches the page management table of FIG. 4 andjudges whether there exists an entry having the same logical address LAas writing data to be transferred from the first memory area 11 (StepST4).

If such an entry is detected, the controller 10 selects this entry andthis process goes to the step ST9. If such an entry is not detected,this process goes to the step ST5.

5. The controller 10 judges whether there exists an unused entry in thepage management table (Step ST5).

If the unused entry is detected, this process goes to the step ST7. Ifthe unused entry is not detected, this process goes to the step ST6.

6. The controller 10 executes “data transfer process from the secondmemory area to the third memory area” (Step ST6). As a result, the entrycorresponding to outputted data is set to be an unused entry. Thecontroller 10 obtains an available unused entry and this process returnsto the step ST5.

7. The controller 10 selects an unused entry as the destination of thewriting data (Step ST7).

8. The controller 10 sets the logical address of the writing data of thepage unit to the selected entry (Step ST8). The selected entry is to betreated as the entry corresponding to the writing data.

9. The controller 10 determines a writing position in the selected entry(Step ST9). The process for determining the writing position isdescribed below.

-   -   9-1. The controller 10 searches the physical block management        table of FIG. 7 or FIG. 8 and selects a block having an empty        page with “write-enable” state used in the second memory area        12. If such a block is detected, the controller 10 selects an        empty page in the block as the destination of the writing data        (Step ST9-1).

In the writing of data by the page unit, if the nonvolatilesemiconductor memory comprising the second memory area 12 can onlyperform writing of data in the ascending order of the physical address,the controller 10 selects an empty page in which data can be appended.

If the empty page is detected in the block used in the second memoryarea 12, this process goes to the step ST10. If the empty page is notdetected in the block used in the second memory area 12, this processgoes to the step ST9-2.

-   -   9-2. The controller 10 searches the physical block management        table of FIG. 7 or FIG. 8 and judges whether there exists a free        block (Step ST9-2). If the free block is detected, this process        goes to the step ST9-4. If the free block is not detected, this        process goes to the step ST9-3.    -   9-3. The controller 10 executes the “data transfer process from        the second memory area to the third memory area” in order to        create a free block (Step ST9-3). After creating the free block,        this process returns to the step ST9-2.    -   9-4. The controller 10 gets the free block for the second memory        area 12 (Step ST9-4).    -   9-5. The controller 10 updates the entry of the physical block        management table of FIG. 7 or FIG. 8 corresponding to the        obtained free block to “second memory area 12 (active)”. In the        second basic configuration (FIG. 8), the controller 10 acquires        an area for storing the page availability, and the area is        associated with the entry (Step ST9-5).    -   9-6. The controller 10 instructs the nonvolatile semiconductor        memory to erase data in the obtained free block, and updates all        the page availability to “write-enable” state. The controller 10        selects one of empty pages in the block as the destination of        the writing data (Step ST9-6).

The process for determining the writing position is completed with abovedescription.

10. The controller 10 judges whether all of sector unit data composingpage unit data exist in the first memory area 11 (Step ST10).

The controller 10 scans sector flags of the entry corresponding to thewriting data in the cache management table of FIG. 3. If all the sectorflags are “1”, this process goes to the step ST12. If any of the sectorflags is “0”, this process goes to the step ST11.

11. If any of the sector flags is “0”, not all sector unit data arecompleted in the first memory area 11. Therefore, the controller 10collects missing data corresponding to the sector position with thesector flag “0” from the second memory area 12 and/or the third memoryarea 13 (Step ST11).

The controller 10 attempts to read out the missing data from the secondmemory area 12.

The controller 10 aligns a logical address of sector unit data by a sizeof the page unit and searches the page management table at the alignedlogical address.

If the entry is detected, the controller 10 reads out the missing dataincluded in page unit data corresponding to the physical addressrecorded in the entry. If the entry is not detected, the controller 10attempts to read out the missing data from the third memory area 13.

The controller 10 aligns a logical address of sector unit data by a sizeof the block unit and searches the block management table at the alignedlogical address.

If the entry is detected, the controller 10 reads out the missing dataincluded in block unit data corresponding to the physical addressrecorded in the entry.

The missing data read out from the second memory area 12 or the thirdmemory area 13 is temporarily stored in a work area of the first memoryarea 11 or the main memory of the controller 10; however, it is notlimited to this.

12. After completing all sector unit data composing page unit data, thecontroller 10 instructs the nonvolatile semiconductor memory to writethe page unit data in the empty page selected as the destination of thewriting data in the second memory area 12. The controller 10 updates thecorresponding page availability in the physical block management tableto “written” state (full: this storage area is filled with valid data)(Step ST12).

After writing the page unit data, the controller 10 registers thelogical address of the writing data and the physical address of the pageas the destination of the writing data in the selected entry of the pagemanagement table.

If a physical address is already stored in the selected entry beforeregistering a new physical address, the controller 10 overwrites thephysical address. The old data which is stored in the page indicated bythe old physical address becomes invalid data.

13. The controller 10 updates the cache management table of FIG. 3. Theentry corresponding to the writing data is rendered invalid state andreleased for input data from the host apparatus (Step ST13).

Subsequently, the controller 10 scans the physical block managementtable of FIG. 7 or FIG. 8 and the page management table of FIG. 4, andexecutes a release process for setting an “active” block, in which allpage unit data are invalid data, to be a “free” block.

Specifically, an entry corresponding to a block which is set to be“active” in the physical block management table and in which a pageindicated by a physical address in the page management table does notexist is set to be “free”. In the configuration of FIG. 8, the area forstoring the page availability is released.

•“Large Unit” Case (See, a Flowchart of FIG. 11, FIG. 13, and FIG. 14)

The controller 10 selects the data to be outputted from the first memoryarea 11 and transfers the selected data to the third memory area 13 asdata of the block unit. The steps on and after the step ST4′ in FIG. 11are referred.

4′. The controller 10 searches the physical block management table ofFIG. 7 or FIG. 8 and gets a free block. The controller 10 allocates theobtained free block to the third memory area 13 (Step ST4′).

The controller 10 updates the entry of the physical block managementtable corresponding to the obtained free block to “third memory area 13(active)” and instructs the nonvolatile semiconductor memory to erasedata in the obtained free block.

If a size of the “large unit” is less than a size of the block unit, thecontroller 10 may select a block having an empty area of the “largeunit” with “write-enable” state used in the third memory area 13, as the“small unit” case.

5′. The controller 10 judges whether all of sector unit data composingblock unit data exist in the first memory area 11 (Step ST5′).

Specifically, the controller 10 judges whether the cache managementtable of FIG. 3 includes all entries corresponding to page unit dataincluded in the logical address range of a size of the block unit, and,at the same time, judges whether all the sector flags of these entriesare “1”.

If all of sector unit data composing block unit data are completed inthe first memory area 11, this process goes to the step ST7′. If not allentries corresponding to page unit data included in the logical addressrange are detected, and/or any of the sector flags is “0”, this processgoes to the step ST6′.

6′. The controller 10 collects the missing data corresponding to thepage position which is not included in the cache management table andthe sector position with the sector flag “0” from the second memory area12 and/or the third memory area 13 (Step ST6′).

The controller 10 attempts to read out the missing data from the secondmemory area 12, as shown in FIG. 13.

The controller 10 aligns a logical address of sector unit data by a sizeof the page unit and searches the page management table at the alignedlogical address.

If the entry is detected, the controller 10 reads out the missing dataincluded in page unit data corresponding to the physical addressrecorded in the entry.

If the entry is not detected, the controller 10 attempts to read out themissing data from the third memory area 13, as shown in FIG. 14.

The controller 10 aligns a logical address of sector unit data by a sizeof the block unit and searches the block management table at the alignedlogical address. The controller 10 reads out the missing data includedin block unit data corresponding to the physical address recorded in theentry.

The missing data read out from the second memory area 12 or the thirdmemory area 13 is temporarily stored in a work area of the first memoryarea 11 or the main memory of the controller 10; however, it is notlimited to this.

7′. After completing all sector unit data composing block unit data, thecontroller 10 instructs the nonvolatile semiconductor memory to writethe block unit data in the empty block selected as the destination ofthe writing data in the third memory area 13 (Step ST7′).

After writing the block unit data, the controller 10 registers thephysical address of the block as the destination of the writing data inthe entry of the block management table corresponding to the logicaladdress range of a size of the block unit.

If a physical address is already stored in the selected entry beforeregistering a new physical address, the controller 10 overwrites thephysical address. The old data which is stored in the block indicated bythe old physical address becomes invalid data.

8′. The controller 10 updates the cache management table of FIG. 3. Theentry corresponding to the writing data is rendered invalid state andreleased for input data from the host apparatus (Step ST8′).

Subsequently, the controller 10 scans the physical block managementtable of FIG. 7 or FIG. 8 and the block management table of FIG. 6, andexecutes a release process for setting an “active” block, in which blockunit data is invalid, to be a “free” block.

Specifically, an entry corresponding to a block which is set to be“active” in the physical block management table and which is notindicated by a physical address in the block management table is set tobe “free”.

Likewise, if an entry, which corresponds to a logical address includedin the logical address range of the writing data of a size of the blockunit, exists in the page management table of FIG. 4 or FIG. 5, the entryis rendered invalid state. On the basis of the transmission of the datastored in the second memory area 12 to the third memory area 13, inorder to invalidate the data stored in the second memory area 12 forprevention of referencing, such process is performed.

Further, in the second memory area 12, the controller 10 sets an“active” block, in which all page unit data are invalid data, to be a“free” block. In the configuration of FIG. 8, the area for storing thepage availability is released.

(b). The controller 10 counts the number of data in the first and secondmemory area 11, 12, and determines to manage the data with either the“large unit” which is equal to the block unit or the “small unit” whichis equal to the page unit.

In this case, the controller 10 searches the cache management table ofFIG. 3 and the page management table of FIG. 4 or FIG. 5, and counts upthe total number of the entries, which are included in the logicaladdress range calculated by aligning a logical address of data to beoutputted by a size of the block unit, in the first and second memoryareas 11, 12.

If the total number of the entries is a predetermined threshold value ormore, such as not less than 50% of the total number of page unit (“smallunits”) data storable in one area of the block unit (“large unit”), thedata to be outputted is managed with the “large unit”, and if the totalnumber of the entries is less than the predetermined threshold value,the data to be outputted is managed with the “small unit” (Step ST1→StepST2→Step ST3).

•“Small Unit” Case (See, the Flowchart of FIG. 10)

The controller 10 stores the data outputted from the first memory area11 in the second memory area 12 as data of the page unit, as in theabove mentioned case “(a)”. After writing the data outputted from thefirst memory area 11 in the second memory area 12, the cache managementtable of FIG. 3 is updated to render the entry, corresponding to thewriting data, invalid state, as in the above mentioned case “(a)”. Inaddition, the page management table of FIG. 4 or FIG. 5 and the physicalblock management table of FIG. 7 or FIG. 8 are updated (Step ST4 to StepST13).

•“Large Unit” Case (See, the Flowchart of FIG. 11)

The controller 10 stores the data outputted from the first memory area11 in the third memory area 13 as data of the block unit, as in theabove mentioned case “(a)”. After writing the data outputted from thefirst memory area 11 in the third memory area 13, the cache managementtable of FIG. 3 is updated to render the entry, corresponding to thewriting data, invalid state, as in the above mentioned case “(a)”. Inaddition, the page management table of FIG. 4 or FIG. 5, the blockmanagement table of FIG. 6, and the physical block management table ofFIG. 7 or FIG. 8 are updated (Step ST4′ to Step ST8′).

In the flowchart of FIG. 11, the step ST4′ may be arranged immediatelybefore the step ST7′. In this case, the controller 10 may allocates a“free” block to the third memory area 13 after determination of the datato be written in the third memory area 13.

C. Data Transfer Process from the Second Memory Area to the Third MemoryArea

The data transfer process from the second memory area 12 to the thirdmemory area 13 is described with reference to FIG. 15.

The capacity of the second memory area 12 is usually set to be smallerthan the capacity of the third memory area 13, and therefore, if acertain amount of data is accumulated in the second memory area 12 (thenumber of blocks, occupied by data of a size of the “small unit” whichis equal to the page unit, exceeds a permissive range defined as thecapacity of the second memory area 12), the controller 10 selects anejection block from the second memory area 12 under the secondcondition.

The controller 10 transfers, each data of a size of the “small unit”which is equal to the page unit stored in the ejection block, to thethird memory area 13, as data of a size of the “large unit” which isequal to the block unit.

In other words, the controller 10 changes the data management unit fromthe “small unit” which is equal to the page unit to the “large unit”which is equal to the block unit. In this process, a plurality offragment “small unit” data included in the logical address range of asize of the “large unit” are collected from the first, second, and thirdmemory areas 11, 12, and 13 and are merged into block unit data(Defragmentation).

The second condition is defined by the writing order or the number ofvalid data. Specifically, the controller 10 executes following process(a) or process (b).

(a). The controller 10 selects a block having the oldest writing orderfrom among the blocks allocated to the second memory area 12. Each pageunit data included in the selected block is merged into block unit data,and then to be written in the third memory area 13. In this case, thecontroller 10 manages the writing order of the blocks in the secondmemory area 12. The writing order information is stored, for example, inthe controller 10, the nonvolatile semiconductor memory, or other memoryunit.

(b). The controller 10 sums, with respect to each block in the secondmemory area 12, the number of page unit data stored in the second memoryarea 12 in a logical address range calculated by aligning, a logicaladdress of valid data of a size of the page unit (“small unit”) in theblock, by a size of the block unit (“large unit”). The controller 10selects the block with the maximum summed value, and each valid data inthe block is merged into block unit data and written in the third memoryarea 13 (Step ST1 to Step ST8).

Hereinafter, the case “(b).” is described.

1. For example, as shown in FIG. 16, the controller 10 aligns thelogical address LA, associated with valid data of a size of the pageunit in each block allocated to the second memory area 12, by a size ofthe block unit (Step ST1).

2. The controller 10 counts up the number of valid data stored in thesecond memory area 12 for each logical address range aligned by a sizeof the block unit (Step ST2). The number of valid data in the logicaladdress ranges X1, X2, and X3 of a size of the block unit arerespectively 3, 2, and 1.

3. The controller 10 sums the number of valid data counted at the stepST2 for each block in the second memory area 12 (Step ST3). Thecontroller 10 does not carry out the double count of the valid data withwhich a logical address overlaps.

With regard to the block Y1 in the second memory area 12, the valid datain the block Y1 is a1 and a4. The valid data a1 is included in thelogical address range X1 of a size of the block unit. In the logicaladdress range X1, there are three valid data a1, a2, and a3 in thesecond memory area 12.

The valid data a4 is included in the logical address range X2 of a sizeof the block unit. In the logical address range X2, there are two validdata a4 and a6 in the second memory area 12.

As a result, with regard to the block Y1 in the second memory area 12,the total number of valid data in the logical address ranges X1 and X2including the valid data a1 and a4 in the physical address range Y1 is5.

With regard to the block Y2, the total number of valid data in thelogical address range X1 including the valid data a2 and a3 in thephysical address range Y2 is 3.

With regard to the block Y3, the total number of valid data in thelogical address ranges X2 and X3 including the valid data a6 and a9 inthe physical address range Y3 is 3.

4. The controller 10 selects valid data in the logical address range ofa size of the block unit including valid data stored in the block inwhich the total number summed at the step ST3 is the largest (Step ST4).

In the case of FIG. 16, the valid data a1, a2, a3, a4, and a6 in thelogical address ranges X1 and X2 of a size of the block unit, includingthe valid data in the physical address range Y1 with the largest totalnumber, are to be written in the third memory area 13.

The following description shows a process for merging page unit data inthe selected block into one block unit data and for writing the blockunit data in the third memory area 13. The following process is repeateduntil all page unit data in the selected block are written in the thirdmemory area 13.

5. The controller 10 searches the physical block management table ofFIG. 7 or FIG. 8, and gets a “free” block as the destination of thewriting data. This free block is allocated to the third memory area 13.The controller 10 updates the entry of the physical bock managementtable of FIG. 7 or FIG. 8 corresponding to the obtained free block to“third memory area 13 (active)” and instructs the nonvolatilesemiconductor memory to erase data in the obtained free block (StepST5).

6. The controller 10 merges page unit data into block unit data.Specifically, the controller 10 collects valid data, included in thelogical address range calculated by aligning the logical address of thepage unit data by a size of the block unit, from the first, second, andthird memory areas 11, 12, and 13 (Step ST6).

The controller 10 searches the cache management table of FIG. 3. If anentry, which corresponds to a logical address of page unit data includedin the logical address range aligned by a size of the block unit, isdetected, the controller 10 reads out all sector unit data with thesector flag “1” in the entry from the first memory area 11.

With regard to a logical address range including valid data which is notread out from the first memory area 11, the controller 10 searches thepage management table of FIG. 4 or FIG. 5. If an entry which correspondsto a logical address of page unit data associated with the logicaladdress range is detected, the controller 10 reads out valid data, whichis not read out from the first memory area 11, included in the page unitdata corresponding to the physical address recorded in the entry, fromthe second memory area 12.

With regard to a logical address range including valid data which is notread out from the first and second memory areas 11 and 12, thecontroller 10 searches the block management table of FIG. 6. Afterdetecting an entry which corresponds to the logical address aligned by asize of the block unit, the controller 10 reads out valid data, which isnot read out from the first and second memory areas 11 and 12, includedin the block unit data corresponding to the physical address recorded inthe entry, from the third memory area 13.

The destination to which valid data read out from the first memory area11, the second memory area 12, and/or the third memory area 13 istemporarily stored is a work area of the first memory area 11 or themain memory of the controller 10; however, it is not limited to this.

7. After completing all sector unit data composing block unit data, thecontroller 10 instructs the nonvolatile semiconductor memory to writethe block unit data in the empty block selected as the destination ofthe writing data (Step ST7).

In a flowchart of FIG. 15, the step ST5 may be arranged immediatelybefore the step ST7. In this case, the controller 10 may allocates a“free” block to the third memory area 13 after determination of the datato be written in the third memory area 13.

After writing the block unit data, the controller 10 registers thephysical address of the block as the destination of the writing data inthe entry of the block management table corresponding to the logicaladdress range of a size of the block unit.

If a physical address is already stored in the selected entry beforeregistering a new physical address, the controller 10 overwrites thephysical address. The old data which is stored in the block indicated bythe old physical address becomes invalid data.

8. The controller 10 invalidates the entries corresponding to thewriting data collected from the first, second, and third memory areas11, 12, and 13 (Step ST8).

The controller 10 updates the cache management table of FIG. 3. Theentry corresponding to the writing data is rendered invalid state andreleased for input data from the host apparatus.

Subsequently, the controller 10 scans the physical block managementtable of FIG. 7 or FIG. 8 and the block management table of FIG. 6, andexecutes a release process for setting an “active” block, in which blockunit data is invalid, to be a “free” block.

Specifically, an entry corresponding to a block which is set to be“active” in the physical block management table and which is notindicated by a physical address in the block management table is set tobe “free”.

Likewise, if an entry, which corresponds to a logical address includedin the logical address range of the writing data of a size of the blockunit, exists in the page management table of FIG. 4 or FIG. 5, the entryis rendered invalid state. On the basis of the transmission of the datastored in the second memory area 12 to the third memory area 13, inorder to invalidate the data stored in the second memory area 12 forprevention of referencing, such process is performed.

Further, in the second memory area 12, the controller 10 sets an“active” block, in which all page unit data are invalid data, to be a“free” block. In the configuration of FIG. 8, the area for storing thepage availability is released.

D. Other

The data transfer process from the first memory area 11 to the secondmemory area 12 and/or the third memory area 13 and the data transferprocess from the second memory area 12 to the third memory area 13, inaddition to the above description, may be performed at a predeterminedtime designated by the host apparatus.

For example, if the semiconductor storage device receives a cache flushcommand, the controller 10 executes the data transfer from the firstmemory area 11 to the second memory area 12 and/or the third memory area13 in accordance with the first condition.

(3) System Example

FIG. 17 shows a system example corresponding to the second basicconfiguration.

A host apparatus 31 executes data transfer with a semiconductor storagedevice 32 according to this embodiment. The host apparatus 31 is, forexample, a personal computer such as a notebook computer. Thesemiconductor storage device 32 is, for example, an SSD as a secondarystorage device mounted in the host apparatus 31.

The semiconductor storage device 32 comprises the first, second, andthird memory areas 11, 12, and 13 and the controller 10 which controlsthese memory areas. The first memory area 11 is included in a volatilesemiconductor memory 21 such as DRAM, and the second and third memoryareas 12 and 13 are included in a nonvolatile semiconductor memory 22such as a NAND type flash memory.

The controller 10 has a CPU and a main memory (for storing a program,management information, and a work area). The controller 10 manages thedata location in the first, second, and third memory areas 11, 12, and13 by translating a logical address to a physical address on the basisof the cache management table, the page management table, the blockmanagement table, and the physical block management table.

The data from the host apparatus 31 is inputted into the semiconductorstorage device 32 through a host I/F (interface) 23. The host apparatus31 executes an access to the semiconductor storage device 32 by thesector unit.

FIG. 18 shows the flow of data from the host apparatus 31.

As described in the above process method, the data from the hostapparatus 31 is stored in the first memory area 11, and thereafter to betransferred to the second memory area 12 or the third memory area 13 inaccordance with the first condition. In addition, the data stored in thesecond memory area 12 is transferred to the third memory area 13 inaccordance with the second condition.

A block in the second memory area 12 and a block in the third memoryarea 13 do not have one-to-one correspondences. On the basis of thephysical block management table, a part of plural blocks in thenonvolatile semiconductor memory 22 is used as the second memory area12, and another part is used as the third memory area 13.

(4) Operation Example

The operation example of this embodiment is described by comparingwriting efficiency with reference to FIG. 18. At the same time, analysisof a size of the management table is described.

A. Comparison of Writing Efficiency

In the following description, the volatile semiconductor memory 21 isassumed to be a DRAM, and the nonvolatile semiconductor memory 22 isassumed to be a NAND type flash memory. A size of the block unit and thepage unit of the NAND type flash memory are respectively assumed to be512 kB and 4 kB, and a size of the sector unit from the host apparatusis assumed to be 512 B. The predetermined threshold value (“the numberof data” or “the data amount”) defined in the first condition is assumedto be 50% (256 kB) of a size of the block unit in the NAND type flashmemory.

The following process is considered: 1 sector unit data Y included inthe logical address range of block unit data X is updated in such astate that the block unit data X is stored in the third memory area 13,and thereafter, the data Y is written in the second memory area 12 orthe third memory area 13 to be made nonvolatile data.

As viewed from the host apparatus 31, the sector unit data Y included inthe logical address range of the block unit data X is rendered updatedstate at the time when the data Y has been stored in the second memoryarea 12 or the third memory area 13.

(a). Operation Example 1

When the data Y is written in the first memory area 11 in the initialstate that there is no data in the first memory area 11, as a result,only sector unit data Y (512 B) exists in the first memory area 11 overthe logical address range of a size of the block unit including the dataY (the logical address range is equal to the logical address range ofthe data X). The controller 10 can detect the data amount by searchingthe cash management table.

The above size 512 B is smaller than 256 kB which is defined as thepredetermined threshold value in the first condition.

The controller 10 transfers the data Y stored in the first memory area11 to the second memory area 12 as page unit data (hereinafter referredto as data P) over the logical address range calculated by aligning thelogical address of the data Y by a size of the page unit.

Since a size of the sector unit data Y is smaller than a size of thepage unit, the missing data is required to be read out from, forexample, the third memory area 13 in order to complete the page unitdata P.

The controller 10 aligns the logical address of the data P by a size ofthe block unit to search the block management table at the alignedlogical address (which is equal to the logical address of the data X).

If an entry corresponding to the logical address is detected, thecontroller 10 examines the physical address at which the data X isstored.

The controller 10 reads out the page unit data, corresponding to thelogical address range of the data P from the data X in the third memoryarea 13, onto the volatile semiconductor memory 21, and creates an imageof the data P by writing the data Y over there.

The controller 10 writes the page unit data P, including the sector unitdata Y, in an empty page in the second memory area 12 and updates thecache management table, the page management table, and the blockmanagement table. The data Y written in the second memory area 12becomes nonvolatile data.

When the data having the same size as the data Y are continuouslywritten, since 1 block unit is composed of 128 page units, thesemiconductor storage device 32 erases one block unit data for theupdating of the data of 128 sector units (for the writing of 128 pages).

In this case, the writing efficiency is 512 kB/(512 B×128)=8, and thewriting efficiency is improved in comparison with the case without usingthis embodiment (512 kB/512 B=1024). In this example, the 1 sector unitdata is updated; however, if the one page unit data is updated, thewriting efficiency is further improved.

In the technique of the patent document presented above, the data blockand the log block have one-to-one correspondences, and therefore, forexample if the data of 128 sectors respectively belonging to a differentblock is updated, 128 blocks are required to be erased.

Alternatively, in this embodiment, the block in the second memory area12 and the block in the third memory area 13 do not have one-to-onecorrespondence. Therefore, even if a plurality of sector unit datastored in a different block are updated, superseding data can be storedin the same block of the second memory area 12 and data erasing amountin this case is only a size of the one block unit.

(b). Operation Example 2

The initial state that, superseding data of 384 kB included in thelogical address range calculated by aligning the logical address of thedata Y by a size of the block unit (the logical address range is equalto the logical address range of the data X) has been already written inthe first memory area 11, is assumed.

In this initial state, when the sector unit data Y which is included inthe logical address range of the data X and not stored in the firstmemory area 11 is written in the first memory area 11, data of (384kB+512 B) including the data Y exists in the logical address range ofthe data X. The controller 10 can detect the data amount by searchingthe cash management table.

The above size (384 kB+512 B) is not smaller than 256 kB which isdefined as the predetermined threshold value in the first condition.

The controller 10 transfers the data of (384 kB+512 B) including thedata Y, which is stored in the first memory area 11, to the third memoryarea 13 as block unit data (hereinafter referred to as data B) over thelogical address range calculated by aligning the logical address of thedata Y by a size of the block unit.

Since a total size of the superseding data and the sector unit data Y issmaller than a size of the block unit, the missing data is required tobe read out from, for example, the third memory area 13 in order tocomplete the block unit data B.

The controller 10 searches the block management table at the logicaladdress of the data B (which is equal to the logical address of the dataX) to detect the physical address at which the data X is stored. Thecontroller 10 reads out the data X from the third memory area 13 ontothe volatile semiconductor 21 and creates image of the data B by writingthe superseding data and the data Y over there.

The controller 10 erases data in a “free” block and allocates the erasedfree block to the third memory area 13. The block unit data B includingthe superseding data and the sector unit data Y is written in thisblock. The cache management table and the block management table areupdated. According to this, the superseding data and the sector unitdata Y written in the third memory area 13 becomes nonvolatile data.

In this case, the semiconductor storage device 32 erases one block unitdata for the updating of the data of about 384 kB (384 kB+512 B).

Therefore, the writing efficiency is 512 kB/384 kB=1.33, and the writingefficiency is improved in comparison with the case where the data ofabout 384 kB is updated by the sector unit (512 kB/512 B=1024).

In this example, the data of about 384 kB is updated; however, if a sizeof the data becomes closer to 512 kB as a size of the block unit, thewriting efficiency is further improved.

B. Size of the Management Table

If the nonvolatile semiconductor memory is managed with the “smallunit”, the controller 10 may execute fine control of the data writinglocation without regard to the data size or the data amount from thehost apparatus 31 and the writing efficiency may be improved. However,the management data for executing the address translation becomes alarge size, whereby the processing efficiency in the controller 10 maybe deteriorated.

Alternatively in this embodiment, the two management units; the “smallunit” and the “large unit” are adopted. By using the management tablesaccording to the data management resolution, the controller 10 suppressthe increase of the number of data managed with the “small unit”.Therefore, the semiconductor storage device 32 according to thisembodiment prevents from the increase of a size of the management tablesand realizes the high writing efficiency.

(5) Other

With respect to the second and third memory areas 12 and 13, thefollowing process may be performed in addition to the process of thisembodiment.

A. Compaction of Second Memory Area

When the number of invalid data in the second memory area 12 isincreased, and when the number of blocks having no page with“write-enable” state is increased, as shown in FIG. 19, the controller10 may collect only valid data and copy these valid data to a freeblock.

As a result, the block in which valid data are originally stored can bereleased, whereby the number of invalid data in the second memory area12 is reduced, and the number of free blocks is increased. This processis called a compaction of the second memory area 12 on the basis thatthe valid data are collected and copied to a free block (a compactionblock).

The writing efficiency may be able to be further improved by thecompaction. However, in this embodiment, in the similar case, the datatransfer process from the second memory area 12 to the third memory area13 can be replaced with the compaction, and therefore, the compaction isauxiliary process.

For example, the controller 10 calculates the number of invalid data ofthe “small unit” for each block in the second memory area 12. Thecontroller 10 sequentially selects a block in descending order of thenumber of invalid data, and thus, the valid data in the selected blockare copied to an erased free block. The block filled with the valid datais allocated to the second memory area 12.

The compaction is performed in the case where the total number ofinvalid data included in the second memory area 12 becomes larger than apredetermined threshold value, for example.

B. Compaction of Third Memory Area

The compaction of the third memory area 13 can be applied in the casewhere a size of the data management unit (“large unit”) in the thirdmemory area 13 is less than a size of the block unit.

When the number of invalid data in the third memory area 13 isincreased, and when the number of blocks having no page with“write-enable” state, as shown in FIG. 19, the controller 10 may collectonly valid data and copy these valid data to a free block.

As a result, the block in which valid data are originally stored can bereleased, whereby the number of invalid data in the third memory area 13is reduced, and the number of free blocks is increased. This process iscalled a compaction of the third memory area 13 on the basis that thevalid data are collected and copied to a free block (a compactionblock).

For example, the controller 10 calculates the number of invalid data ofthe “large unit” for each block in the third memory area 13. Thecontroller 10 sequentially selects a block in descending order of thenumber of invalid data, and thus, the valid data in the selected blockare copied to an erased free block. The block filled with the valid datais allocated to the third memory area 13.

The compaction is performed in the case where the total number ofinvalid data included in the third memory area 13 becomes larger than apredetermined threshold value, for example.

3. Summary

According to this embodiment, the following configuration can realizethe improvement of the writing efficiency and the prevention of theperformance deterioration and of the life shortening, regardless thedata size or the data amount from the host apparatus.

•Allocation of Storage Locations

A semiconductor storage device includes a first memory area configuredin a volatile semiconductor memory which performs writing of data by afirst unit or less, the first unit is an access unit to thesemiconductor storage device, second and third memory areas configuredin a nonvolatile semiconductor memory which performs writing of data bya second unit and performs erasing of data by a third unit, the thirdunit is twice or larger natural number times as large as the secondunit, and a controller executing following processing.

The controller executes a first processing for storing a plurality ofdata by the first unit in the first memory area, and a second processingfor storing data outputted from the first memory area by a firstmanagement unit in the second memory area, the first management unit istwice or larger natural number times as large as the first unit and isless than the third unit, and a third processing for storing dataoutputted from the first memory area by a second management unit in thethird memory area, the second management unit is twice or larger naturalnumber times as large as the first management unit.

•Data Transfer from Second Memory Area to Third Memory Area(Defragmentation)

The controller further executes a fourth processing for selecting dataof the first management unit to be outputted from the second memoryarea, and a fifth processing for storing data including the selecteddata by the second management unit in the third memory area.

•Sharing Memory

The second and third memory areas share the same nonvolatilesemiconductor memory, and the controller allocates areas of the thirdunit to the second and third memory areas respectively.

•Allocation Condition 1 (the Number of Data in First Memory Area)

The controller calculates logical address range by aligning logicaladdress of data to be outputted from the first memory area into thesecond management unit, counts a number of data which is included in thelogical address range and is stored in the first memory area, executesthe second processing if the number of data is less than a predeterminedthreshold value, and executes the third processing if the number of datais the predetermined threshold value or more.

Allocation Condition 2 (the Number of Data in First And Second MemoryAreas)

The controller calculates logical address range by aligning logicaladdress of data to be outputted from the first memory area into thesecond management unit, counts a number of data which is included in thelogical address range and is stored in the first and second memoryareas, executes the second processing if the number of data is less thana predetermined threshold value, and executes the third processing forif the number of data is the predetermined threshold value or more.

•Trigger of Defragmentation

The controller executes the fourth and fifth processing if a number ofareas of the third unit occupied by a plurality of valid and invaliddata stored in the second memory area exceeds a permissible range.

•Defragmentation Condition 1 (Old Data)

In the fourth processing, the controller detects an area of the thirdunit having the oldest writing order in the second memory area, andselects each valid data of the first management unit stored in the areaof the third unit.

•Defragmentation Condition 2 (Valid Data)

In the fourth processing, the controller calculates logical addressrange by aligning logical address of valid data into the secondmanagement unit for each area of the third unit in the second memoryarea, counts a number of valid data which is included in the logicaladdress range and is stored in the second memory area, totals the numberof valid data for each area of the third unit in the second memory area,detects an area of the third unit having the largest total number, andselects each valid data of the first management unit stored in the areaof the third unit.

•Defragmentation Condition 3 (Invalid Data)

In the fourth processing, the controller counts a number of invalid datafor each area of the third unit in the second memory area, detects anarea of the third unit having the smallest number of invalid data, andselects each valid data of the first management unit stored in the areaof the third unit.

•The Data Management Unit in the Second Memory Area: Small

The second unit is twice or larger natural number times as large as thefirst management unit.

•The Data Management Unit in the Second Memory Area: Large

The first management unit is twice or larger natural number times aslarge as the second unit, and the third unit is twice or larger naturalnumber times as large as the first management unit.

•The Data Management Unit in the Third Memory Area: Small

The third unit is twice or larger natural number times as large as thesecond management unit.

•The Data Management Unit in the Third Memory Area: Large

The second management unit is twice or larger natural number times aslarge as the third unit.

•Invalidation of the Second Memory Area

In the second processing, the controller writes new data of the firstmanagement unit in empty areas of the second unit in the second memoryarea, sets old data stored in the second memory area invalid if logicaladdress of the new data corresponds to logical address of the old data,treats the new data as valid data which has priority over the old data,and treats the old data as invalid data which is ignored by referring tothe new data.

•Compaction of the Second Memory Area

The controller judges whether a number of invalid data in the secondmemory area exceeds a predetermined threshold value, counts a number ofinvalid data for each area of the third unit in the second memory area,selects valid data in areas of the third unit in order from the one withthe largest number of invalid data, rewrites the selected valid data ina first area of the third unit, the first area is empty, allocates thefirst area to the second memory area after rewriting the selected validdata therein, and releases a second area of the third unit in the secondmemory area, the second area has no valid data by rewriting the selectedvalid data in the first area.

•Invalidation of the Third Memory Area

In the third processing, the controller writes new data of the secondmanagement unit in an empty area of the third unit in the third memoryarea, sets old data stored in the third memory area invalid if logicaladdress of new data corresponds to logical address of the old data,treats the new data as valid data which has priority over the old data,and treats the old data as invalid data which is ignored by referring tothe new data.

•Compaction of the Third Memory Area

The controller judges whether a number of invalid data in the thirdmemory area exceeds a predetermined threshold value, counts a number ofinvalid data of the second management unit for each area of the thirdunit in the third memory area, selects valid data in areas of the thirdunit in order from the one with the largest number of invalid data,rewrites the selected valid data of the second management unit in emptyarea of the third unit in the third memory area, and releases an area ofthe third unit. The second management unit is less than the third unit.

4. Application Example

The semiconductor storage device according to this embodiment may beapplied to, for example, an SSD used as a secondary storage device in apersonal computer such as a notebook computer. A specific example inthis case is described later.

5. Conclusion

According to this embodiment, the semiconductor storage device using thenonvolatile semiconductor memory in which the unit of erasing, reading,and writing is specified can realize the improvement of the writingefficiency and the prevention of the performance deterioration and ofthe life shortening, regardless the data size or the data amount fromthe host apparatus.

The present invention is not limited to the above-described embodiments,and the components can be modified and embodied without departing fromthe spirit and scope of the invention. Various inventions can be formedby the appropriate combinations of a plurality of components disclosedin the above-described embodiments. For example, several components maybe omitted from all the components disclosed in the embodiments, or thecomponents over the different embodiments may be suitably combined witheach other.

II. Semiconductor Storage Device for Preventing the Increase of ErasingCount 1. Outline

The compaction described in the section I. is excellent in the effectiveutilization of a storage area based on the erasure of invalid data.However, the compaction requires copy operation that the identical datais written to other block, and therefore, there generate a side effectthat, when the valid data subjected to the compaction is immediatelyupdated, the erasing count of the blocks increases.

The block newly used by the compaction is filled with valid data;however, when the data subjected to the compaction is updated, the databecomes invalid data. In addition, when the number of invalid data inthe block increases, the valid data in the block again becomes to besubjected to the compaction. As a result, the erasing count of the blockmay increase.

According to the above configuration, the data to be subjected to thecompaction preferably has a low updating frequency, and means fordiscriminating data is required.

On the basis of the above knowledge, in the present embodiments, meansfor discriminating data having a high updating frequency from datahaving a low updating frequency is provided, and the data having a lowupdating frequency becomes a target to be subjected to the compaction,whereby the data to be subjected to the compaction is prevented frombeing immediately updated.

According to this configuration, the erasing count of the blocks isreduced in order to prevent the deterioration of memory cells.

As a specific configuration, following memory areas are provided.

-   -   a first memory area in a volatile semiconductor memory, which        performs reading and writing of data by the first unit or less;    -   a second memory area composed of areas of the third unit in a        nonvolatile semiconductor memory, which performs reading and        writing of data by the second unit and performs erasing of data        by the third unit, and managed with the “small unit (first        management unit)”, a size of the “small unit” being natural        number times as large as a size of the first unit;    -   a third memory area composed of areas of the third unit in a        nonvolatile semiconductor memory, which performs reading and        writing of data by the second unit and performs erasing of data        by the third unit, and managed with the “large unit (second        management unit)”, a size of the “large unit” being twice or        larger natural number times as large as a size of the “small        unit” and being natural number times as large as a size of the        third unit; and    -   a fourth memory area composed of areas of the third unit in a        nonvolatile semiconductor memory, which performs reading and        writing of data by the second unit and performs erasing of data        by the third unit, and managed with the “small unit”, a size of        the “small unit” being natural number times as large as a size        of the first unit.

The fourth memory area is used as means for discriminating data having ahigh updating frequency from data having a low updating frequency.Roughly, in addition to the basic configuration described in the sectionI., the fourth memory area is provided to discriminating data having ahigh updating frequency from data having a low updating frequency.

A plurality of data of the first unit is written in the first memoryarea, and then to be written in the third memory area or the fourthmemory area. The fourth memory area has an FIFO (First-In First-Out)structure. When the number of “active” areas of the third unit used forthe fourth memory area becomes larger than a permissive range, validdata, which satisfies a third condition and is stored in an area of thethird unit having the oldest allocation order in the second memory area,is transferred to the third memory area as “large unit” data.

The area of the third unit having the oldest allocation order in thesecond memory area including valid data, which does not satisfy thethird condition, is moved to the second memory area. When the number of“active” areas of the third unit used for the second memory area becomeslarger than a permissive range and a fourth condition is satisfied,valid data in the second memory area is selected and copied to an emptyarea of the third unit. The area of the third unit filled with validdata is allocated to the second memory area (Compaction).

The principle that a target to be subjected to the compaction in thesecond memory area becomes the data having a low updating frequency isas follows.

Since the fourth memory area has the FIFO structure of the third unit,the data inputted to the fourth memory area stays in the fourth memoryarea for a certain period. Therefore, the data having a high updatingfrequency is updated in the fourth memory area. When the data isupdated, the old data becomes invalid data, and since the supersedingdata is newly inputted to the fourth memory area, the data having a highupdating frequency stays in the fourth memory area without beingoutputted.

The valid data in the second memory area is made a target to besubjected to the compaction, and the valid data in the fourth memoryarea is not made a target to be subjected to the compaction, whereby thedata having a low updating frequency can be made a target to besubjected to the compaction. As a result, it is possible to prevent theincrease of erasing count for blocks as a side effect of the compaction.

2. Embodiments (1) First Embodiment

FIG. 20 shows a semiconductor storage device according to a firstembodiment.

A first memory area 11 temporarily stores data from a host apparatus.The data is written by the sector unit (the first unit) or less in thefirst memory area 11. The first memory area 11 is configured in avolatile semiconductor memory such as a DRAM.

A second memory area 12 is composed of blocks in a nonvolatilesemiconductor memory 22. In the nonvolatile semiconductor memory 22, theunit in which reading/writing is executed at one time is a page (thesecond unit) and the unit in which erasing is executed at one time is ablock (the third unit). A size of the block unit is natural number timesas large as a size of the page unit. The second memory area 12 storesdata by the “small unit” which is equal to the page unit.

A third memory area 13 is composed of blocks in the nonvolatilesemiconductor memory 22 and stores data by the “large unit” which isequal to the block unit.

A fourth memory area 14 is composed of blocks in the nonvolatilesemiconductor memory 22 and stores data by the “small unit” which isequal to the page unit.

The storage capacity of the first memory area 11 is assumed to be largerthan a size of the one block unit in the nonvolatile semiconductormemory 22, and the storage capacity of the nonvolatile semiconductormemory 22 is assumed to be larger than the storage capacity provided asthe product specification of the semiconductor storage device (forexample, SSD).

The storage capacity of the nonvolatile semiconductor memory 22 isallocated to the second, third, and fourth memory areas 12, 13, and 14as follows.

The storage capacity, which is the same as or larger than the storagecapacity provided as the product specification of the semiconductorstorage device, is allocated to the third memory area 13.

The storage capacity remaining by subtracting the storage capacity ofthe third memory area 13 from the storage capacity of the nonvolatilesemiconductor memory 22 is allocated to the second and fourth memoryareas 12 and 14. Each storage capacity of the second and fourth memoryareas 12 and 14 and the rate between them are not limited.

The second, third, and fourth memory areas 12, 13, and 14 are composedof, for example, one or more blocks in the nonvolatile semiconductormemory 22, such as a NAND type flash memory.

The first, second, and third units representing a size of data do notinclude redundant data (ECC, internal control flag, etc.) which is addedto main data from the host apparatus in the semiconductor storagedevice.

In general, the system including the nonvolatile semiconductor memory,for example a NAND type flash memory, executes reading/writing in thestate of adding redundant data to the main data. However, forsimplifying the explanation, each of the units is assumed above.

A controller 10 has a CPU and a main memory, and can operate a programfor executing data management. In this embodiment, the functionsrealized by the controller 10 can be implemented as any of hardware andsoftware or the combination of the both. Whether these functions areimplemented as hardware or software depends on the practical embodimentor the design constraints imposed on the entire system.

When the main memory of the controller 10 is comprised of a volatilesemiconductor memory such as DRAM, the first memory area 11 may beconfigured in the main memory of the controller 10.

The controller 10 includes a cache management table, a page managementtable, a block management table, a page FIFO management table, and aphysical block management table in order to manage where data accessedby the logical address from the host apparatus is stored in the first,second, third and fourth memory areas 11, 12, 13, and 14. Thesemanagement tables are expanded onto the main memory of the controller 10during the operation of the semiconductor storage device.

——Cache Management Table——

FIG. 21 shows an example of a cache management table.

The cache management table controls data stored in the first memory area11 of FIG. 20 by the “small unit” which is equal to the page unit. Thecontrol of the valid data is executed by the sector unit.

It is assumed that one entry is assigned to one area of one page unit inthe first memory area 11.

The number of entries is assumed to be the number of page unit datawhich can be contained within the first memory area 11, that is, notlarger than (the total capacity of the first memory area 11)/(a size ofthe page unit).

A logical address of page unit data, a physical address of the firstmemory area 11, and a sector flag indicating the location of the validdata in the relevant area of the page unit are associated with eachentry.

The area of the page unit for temporarily storing data corresponded toeach entry is provided in the first memory area 11, and the physicaladdress of the area is stored in each entry. If the physical address ofthe area corresponding to the entry is specified, such as if the areasof the page unit are continuously disposed, the physical address is notrequired to be stored in the entry.

The each area of the page unit in the first memory area 11 is furtherdivided into areas of the sector unit in the cache management table. Adata status in each area of the sector unit is represented by settingthe value of the sector flags as “1” or “0”.

In an area with the sector flag of “1”, valid data from the hostapparatus is stored. In an area with the sector flag of “0”, the latestdata written from the host apparatus is not stored, whereby the area istreated as an invalid area. The entry in which all sector flags are “0”is regarded to be an unused entry.

The configuration of the above cache management table is based on acontrol method called a full associative method in which the logicaladdress is allocated to each entry. However, the correspondence betweenthe logical address and the physical address in the first memory area 11may be controlled by an n-way set associative method or the like.

——Page Management Table——

FIG. 22 shows an example of a page management table.

The page management table controls data stored in the second and fourthmemory areas 12 and 14 of FIG. 20 by the “small unit” which is equal tothe page unit.

It is assumed that one entry is assigned to one block in the second andfourth memory areas 12 and 14.

The number of entries is assumed to be provided with allowance, in orderto register the blocks in processing, to the number of blocks which canbe contained within the second and fourth memory areas 12 and 14, thatis, the number providing an allowance to [(the total capacity of thesecond and fourth memory areas 12 and 14)/(a size of the block unit)].

The physical address of the block allocated to the second memory area 12or the fourth memory area 14 is associated with each entry, and thelogical addresses of page unit data in the block are recorded in eachentry.

A page availability is configured to be able to distinguish“write-enable” state (this storage area is empty) from “write-inhibit”state (this storage area is invalid because old data has once writtentherein and new data is written in another storage area) for each page.

——Block Management Table——

FIG. 23 shows an example of a block management table.

The block management table controls data stored in the third memory area13 of FIG. 20 by the “large unit” which is equal to the block unit.

It is assumed that one entry is assigned to one area of one block unitin the third memory area 13.

The number of entries is assumed to be the number of block unit datawhich can be contained within the third memory area 13, that is, notlarger than (the total capacity of the third memory area 13)/(a size ofthe block unit).

Each entry is arranged in order of a logical address. A Physical addresswhich corresponds to a logical address of block unit data and designatesa block in the third memory area 13 is associated with each entry.

——Page FIFO Management Table——

FIG. 24 shows an example of a page FIFO management table.

The page FIFO management table controls data in the blocks allocated tothe fourth memory area 14 of FIG. 20.

It is assumed that one entry is assigned to one block in the fourthmemory area 14.

The number of entries is assumed to be the number of blocks which can beallocated to the fourth memory area 14, that is, (the total capacity ofthe fourth memory area 14)/(a size of the block unit).

The fourth memory area 14 is managed with the FIFO (First-In First-Out)structure of the block unit by using the page FIFO management table.

An entry corresponding to a block newly allocated (inputted) to thefourth memory area 14 is added to the top (the entrance side) of thepage FIFO management table, and entries originally registered in thepage FIFO management table are shifted backward one by one.

When the number of entries exceeds a permissive range, the block havingthe oldest allocation order associated with the entry at the bottom (theexit side) of the page FIFO management table is outputted from thefourth memory area 14.

——Physical Block Management Table——

FIG. 25 shows an example of a physical block management table.

The physical block management table controls the usage of blocks in thenonvolatile semiconductor memory 22.

It is assumed that one entry is assigned to one block (physical block)in the second, third, and fourth memory area 12, 13, and 14. The numberof entries is assumed to be the number of blocks which can be used as adata area.

Each entry is associated with a physical address of a block and storesthe usage of the block (whether the storage area (block) is used as thesecond, third, and fourth memory areas (active) or is unused (free)).

A process flow executed by the controller 10 of FIG. 20 is described.

The controller 10 first writes sector unit (first unit) data from thehost apparatus in the first memory area 11 and stores the data for acertain period therein. With regard to this data store process, “A. Datastore process in the first memory area” described in the section I. canbe applicable.

The controller 10 distinguishes whether the data stored in the firstmemory area 11 should be managed with the “small unit (first managementunit)” or the “large unit (second management unit)”, based on apredetermined condition (which may be substantially the same as thefirst condition of “B. Data output process from the first memory area”described in the section I.).

A size of the “small unit” is a natural number times as large as a sizeof the page unit or a size of the page unit is a natural number times aslarge as a size of the “small unit”.

A size of the “large unit” is twice or larger natural number times aslarge as a size of the “small unit”, and at the same time, is a naturalnumber times as large as a size of the block unit.

In this embodiment, to simplify the explanation, each of the units usedin management tables is assumed below:

A size of the “small unit” which is a data management unit in the secondand fourth memory areas 12 and 14 is equal to a size of the page unit(second unit). A size of the “large unit” which is a data managementunit in the third memory area 13 is equal to a size of the block unit(third unit).

However, a page is controlled by being divided, specifically, a size ofthe “small unit” may be a natural number times as large as a size of thesector unit and a size of the page unit may be twice or larger naturalnumber times as large as a size of the “small unit”.

Alternatively, plural pages are collectively controlled, specifically, asize of the “small unit” may be twice or larger natural number times aslarge as a size of the page unit and a size of the block unit may betwice or larger natural number times as large as a size of the “smallunit”.

Likewise, plural blocks are collectively controlled, specifically, asize of the “large unit” may be twice or larger natural number times aslarge as a size of the block unit.

The above relation between the units may be set as following example:the sector unit (first unit)<the “small unit”<the page unit (secondunit)<the block unit (third unit) 5 the “large unit”.

If the data stored in the first memory area 11 is managed with the“small unit”, the data is transferred to the fourth memory area 14. Ifthe data stored in the first memory area 11 is managed with the “largeunit”, the data is transferred to the third memory area 13.

This data output process is substantially the same as “B. Data outputprocess from the first memory area” described in the section I. However,different from the section I., the destination of the “small unit” datais the fourth memory area 14.

A. FIFO Process in the Fourth Memory Area

As already described, the fourth memory area 14 has the FIFO structureof the block unit. FIG. 26 shows FIFO process in the fourth memory area14.

1. The controller 10 refers to entries of the page management tablecorresponding to a block prepared for writing data in appending manner(hereinafter referred to as a physical block for page-append). Thecontroller 10 stores data outputted from the first memory area 11, asdata of the “small unit” which is equal to the page unit, in a page ofwrite-enable state of the physical block for page-append (Step ST1).

The controller 10 searches the cache management table and judges whetherall of sector unit data composing page unit data, which are determinedto be outputted, exist in the first memory area 11.

If not all sector unit data are completed in the first memory area 11,the controller 10 collects missing data from the second, third, andfourth memory areas 12, 13, and 14.

After completing all sector unit data composing page unit data, thecontroller 10 instructs the nonvolatile semiconductor memory 22 to writethe page unit data.

2. The controller 10 updates the logical address, recorded in the entrycorresponding to the page in which the page unit data has been written,in the page management table (Step ST2). The old data included in thesame logical address range, which had been written in the second andfourth memory areas 12 and 14, becomes invalid data.

3. The controller 10 judges whether there exits an empty page in thephysical block for page-append (Step ST3). If the empty page is notdetected, this process goes to the step ST4. If the empty page isdetected, this process returns to the step ST1.

4. The controller 10 shifts the entries of the page FIFO managementtable backward one by one, and adds the physical address of the physicalblock for page-append to the entry at the top of the page FIFOmanagement table (Step ST4). As a result, the physical block forpage-append is allocated to the fourth memory area 14.

5. The controller 10 executes the following process P1 for the blockhaving the oldest allocation order associated with the entry at thebottom of the page FIFO management table overflowing from the page FIFOmanagement table (Step ST5).

B. Process P1

FIG. 27 shows the flowchart of process P1.

1. The controller 10 searches the page management table of FIG. 22 anddetects the entry in which the physical address of the block overflowingfrom the fourth memory area 14 is recorded (Step ST1).

2. The controller 10 specifies the logical addresses of page unit datarecorded in the entry (Step ST2). The following process is applied toeach logical address.

3. The controller 10 aligns the logical address of the page unit data bya size of the “large unit” which is equal to the block unit, and countsup the number of logical addresses included in the logical address rangealigned by a size of the block unit in the page management table (StepST3).

Incidentally, “the logical address is aligned by a predetermined size(such as a size of the page unit or the block unit)” means that thelogical address is rounded down to such an address that a reminder whenthe logical address is divided by the predetermined size is 0. Forexample, an address calculated by aligning the logical address A by thesize S is (A−(a remainder when A is divided by S)). Similarly, “thelogical address range aligned by a predetermined size” means that therange of the predetermined size from the address calculated by aligningthe logical address by the predetermined size.

If the controller 10 counts up the number of logical addresses only inthe entry having the physical address included in the page FIFOmanagement table, the number of page unit data stored in the fourthmemory area 14 is acquired. On the other hand, if the controller 10 doesnot limit the entry, the number of page unit data stored in the secondand fourth memory areas 12 and 14 is acquired. The controller 10 canselect either condition.

4. The controller 10 judges whether the number of logical addressescounted at the step ST3 is a predetermined threshold value or more (thethird condition). For example, the predetermined threshold value may beset to be 50% of the total number of page unit (“small unit”) datastorable in one area of the block unit (“large unit”)(Step ST4).

If the number of logical addresses counted in the step ST3 is less thanthe predetermined threshold value, this process goes to the step ST5. Ifthe number of logical addresses counted in the step ST3 is not less thanthe predetermined threshold value, this process goes to the step ST6.

5. The controller 10 does not do anything to the page unit data. Thatis, the page unit data stays in the block overflowing from the fourthmemory area 14 (Step ST5).

6. The controller 10 transfers the page unit data to the third memoryarea 13, as data of a size of the “large unit” which is equal to theblock unit (Step ST6).

The controller 10 merges the page unit data into the block unit data, bycollecting valid data included in the logical address range aligned by asize of the block unit, from the first, second, third, and fourth memoryareas 11, 12, 13, and 14 (Defragmentation).

After completing valid data composing the block unit data, thecontroller 10 instructs the nonvolatile semiconductor memory 22 to writethe block unit data in an empty block of the third memory area 13.

7. The controller 10 invalidates the data, which are included in thelogical address range of the writing data, in the first, second, third,and fourth memory areas 11, 12, 13, and 14 (Step ST7).

If all the data in a block becomes invalid data, the controller 10releases the block and sets the status of the block to be “free” statefrom “active” state in the physical block management table.

8. The controller 10 judges whether all logical addresses in the entryhave been processed (Step ST8). If all logical addresses in the entryhave been processed, this process is completed. If not all logicaladdresses in the entry have been processed, this process returns to thestep ST3.

After completing the process P1, if valid data remains in the blockwhich overflowed from the fourth memory area 14, the controller 10 setsthe entry corresponding to the block to be “second memory area 12(active)” in the physical block management table.

In the data transfer from the fourth memory area 14 to the second memoryarea 12, the controller 10 only updating the page FIFO management tableand the physical block management table without instructing thenonvolatile semiconductor memory 22 to read/write data (Move process).

If there exits no empty page in the physical block for page-append, thecontroller 10 gets a free block by searching the physical blockmanagement table. After erasing data in the free block, this block isnewly allocated to a physical block for page-append. The controller 10searches an unused entry in the page management table. The physicaladdress corresponding to the physical block for page-append is recordedin the unused entry.

According to the movement of the blocks from the fourth memory area 14,the number of blocks managed with the page unit is increased in thesecond memory area 12. If the number of blocks in the second memory area12 exceeds a permissive range, that is, the predetermined number ofblocks defined as the capacity of the second memory area 12, thecontroller 10 executes the compaction or the data transfer process fromthe second memory area 12 to the third memory area 13 by the followingprocedures.

C. Process Example 1

FIG. 28 shows the flowchart of process example 1.

1. The controller 10 scans the page management table and counts up thenumber of data (the number of logical addresses) of the “small unit”which is equal to the page unit stored in the second memory area 12(Step ST1).

At the step ST1, the entry with the physical address included in thepage FIFO management table and the entry corresponding to the physicalblock for page-append are not targets to be scanned. Namely, thecontroller 10 only scans the second memory area 12.

2. The controller 10 judges whether the total number of the valid dataof the page unit stored in the second memory area 12 is not larger thana predetermined threshold value (the fourth condition). For example, thepredetermined threshold value may be the number of page unit datastorable in the second memory area 12 (Step ST2).

If the total number of the valid data is larger than the predeterminedthreshold value, since the number of blocks in the second memory area 12can not be decreased, by the compaction, to the permissive range, thisprocess goes to the step ST3. If the total number of the valid data isnot larger than the predetermined threshold value, this process goes tothe step ST6.

3. The controller 10 selects valid data in the second memory area 12based on a predetermined condition and transfers the selected data tothe third memory area 13 as data of the “large unit” which is equal tothe block unit (Step ST3). For example, the predetermined condition maybe substantially the same as the second condition of “C. Data transferprocess from the second memory area to the third memory area” (describedin the section I.).

The controller 10 merges the valid data of the page unit into the blockunit data, by collecting valid data included in the logical addressrange aligned by a size of the block unit, from the first, second,third, and fourth memory areas 11, 12, 13, and 14 (Defragmentation).

After completing valid data composing the block unit data, thecontroller 10 instructs the nonvolatile semiconductor memory 22 to writethe block unit data in an empty block of the third memory area 13.

4. The controller 10 invalidates the data, which are included in thelogical address range of the writing data, in the first, second, third,and fourth memory areas 11, 12, 13, and 14 (Step ST4).

If all the data in a block becomes invalid data, the controller 10releases the block and sets the status of the block to be “free” statefrom “active” state in the physical block management table.

5. The controller 10 judges whether the number of blocks in the secondmemory area 12 is the predetermined number of blocks defined as thecapacity of the second memory area 12 or less (Step ST5).

If the number of blocks in the second memory area 12 is thepredetermined number of blocks defined as the capacity of the secondmemory area 12 or less, this process is completed. If the number ofblocks in the second memory area 12 is larger than the predeterminednumber of blocks defined as the capacity of the second memory area 12,this process returns to the step ST1.

6. The controller 10 gets a free block by searching the physical blockmanagement table. After erasing data in the free block, this block isallocated to a compaction block. The controller 10 searches an unusedentry in the page management table. The physical address of thecompaction block is associated with the unused entry (Step ST6).

7. The controller 10 sequentially selects valid data of the page unit inorder from the block with the smallest number of the valid data in thesecond memory area 12 (Step ST7). The selected valid data is copied tothe compaction block and the logical addresses in the entry of the pagemanagement table corresponding to the compaction block are updated tothe logical addresses of the copied data.

The controller 10 allocates the compaction block filled with the validdata to the second memory area 12 by updating the entry of the physicalblock management table to “second memory area 12 (active)”.

At the step ST7 (the compaction), the latest valid data included in thelogical address range of the copied data may be read out from the firstmemory area 11 and the copied data may be overwritten with the latestvalid data. The sector unit data in the first memory area 11 taken intothe copied data is rendered invalid state.

8. The controller 10 invalidates the data, which has the same logicaladdress as the copied data, in the second memory area 12 (Step ST8). Ifall the data in a block becomes invalid data, the controller 10 releasesthe block and sets the status of the block to be “free” state from“active” state in the physical block management table.

9. The controller 10 judges whether the number of blocks in the secondmemory area 12 is the predetermined number of blocks defined as thecapacity of the second memory area 12 or less (Step ST9).

If the number of blocks in the second memory area 12 is thepredetermined number of blocks defined as the capacity of the secondmemory area 12 or less, this process is completed. If the number ofblocks in the second memory area 12 is larger than the predeterminednumber of blocks defined as the capacity of the second memory area 12,this process returns to the step ST6.

D. Process Example 2

FIG. 29 shows the flowchart of process example 2.

1. The controller 10 scans the page management table and selects twoblocks with the smallest number of the valid data (the number of logicaladdresses) of the “small unit” which is equal to the page unit (StepST1).

At the step ST1, the entry with the physical address included in thepage FIFO management table and the entry corresponding to the physicalblock for page-append are not targets to be scanned. Namely, thecontroller 10 only scans the second memory area 12.

2. The controller 10 judges whether the total number of the valid dataof the page unit in the selected two blocks is not larger than apredetermined threshold value (for example, the number of page unit datacontained in the third unit) (the fourth condition) (Step ST2).

If the total number of the valid data is larger than the predeterminedthreshold value, since the number of blocks in the second memory area 12may not be decreased, by the compaction, to the permissive range, thisprocess goes to the step ST3. If the total number of the valid data isnot larger than the predetermined threshold value, this process goes tothe step ST6.

3. The controller 10 selects valid data in the second memory area 12based on a predetermined condition and transfers the selected data tothe third memory area 13 as data of the “large unit” which is equal tothe block unit (Step ST3). For example, the predetermined condition maybe substantially the same as the second condition of “C. Data transferprocess from the second memory area to the third memory area” (describedin the section I.).

The controller 10 merges the valid data of the page unit into the blockunit data, by collecting valid data included in the logical addressrange aligned by a size of the block unit, from the first, second,third, and fourth memory areas 11, 12, 13, and 14 (Defragmentation).

After completing valid data composing the block unit data, thecontroller 10 instructs the nonvolatile semiconductor memory 22 to writethe block unit data in an empty block of the third memory area 13.

4. The controller 10 invalidates the data, which are included in thelogical address range of the writing data, in the first, second, third,and fourth memory areas 11, 12, 13, and 14.

If all the data in a block becomes invalid data, the controller 10releases the block and sets the status of the block to be “free” statefrom “active” state in the physical block management table (Step ST4).

5. The controller 10 judges whether the number of blocks in the secondmemory area 12 is the predetermined number of blocks defined as thecapacity of the second memory area 12 or less (Step ST5).

If the number of blocks in the second memory area 12 is thepredetermined number of blocks defined as the capacity of the secondmemory area 12 or less, this process is completed. If the number ofblocks in the second memory area 12 is larger than the predeterminednumber of blocks defined as the capacity of the second memory area 12,this process returns to the step ST1.

6. The controller 10 gets a free block by searching the physical blockmanagement table. After erasing data in the free block, this block isallocated to a compaction block. The controller 10 searches an unusedentry in the page management table. The physical address of thecompaction block is associated with the unused entry (Step ST6).

7. The controller 10 sequentially selects valid data of the page unit inorder from the block with the smallest number of the valid data in thesecond memory area 12 (Step ST7). The selected valid data is copied tothe compaction block and the logical addresses in the entry of the pagemanagement table corresponding to the compaction block are updated tothe logical addresses of the copied data.

The controller 10 allocates the compaction block filled with the validdata to the second memory area 12 by updating the entry of the physicalblock management table to “second memory area 12 (active)”.

At the step ST7, the latest valid data included in the logical addressrange of the copied data may be read out from the first memory area 11and the copied data may be overwritten with the latest valid data. Thesector unit data in the first memory area 11 taken into the copied datais rendered invalid state.

8. The controller 10 invalidates the data, which has the same logicaladdress as the copied data, in the second memory area 12 (Step ST8). Ifall the data in a block becomes invalid data, the controller 10 releasesthe block and sets the status of the block to be “free” state from“active” state in the physical block management table.

9. The controller 10 judges whether the number of blocks in the secondmemory area 12 is the predetermined number of blocks defined as thecapacity of the second memory area 12 or less (Step ST9).

If the number of blocks in the second memory area 12 is thepredetermined number of blocks defined as the capacity of the secondmemory area 12 or less, this process is completed. If the number ofblocks in the second memory area 12 is larger than the predeterminednumber of blocks defined as the capacity of the second memory area 12,this process returns to the step ST6.

In the step ST1 of the process example 2, although the two blocks withthe smallest number of valid data are selected, the number is notlimited to two, and two or more blocks may be selected.

In addition, the “predetermined threshold value” in the step ST2 of theprocess example 2, may be set the number of page unit data storable inthe blocks smaller by one than the number of the selected blocks.

(2) Second Embodiment

FIG. 30 shows a semiconductor storage device according to a secondembodiment.

A size of the “small unit” is a natural number times as large as a sizeof the page unit or a size of the page unit is a natural number times aslarge as a size of the “small unit”.

A size of the “large unit” is twice or larger natural number times aslarge as a size of the “small unit”, and at the same time, a size of theblock unit is twice or larger natural number times as large as a size ofthe “large unit”.

However, a page is controlled by being divided, specifically, a size ofthe “small unit” may be a natural number times as large as a size of thesector unit and a size of the page unit may be twice or larger naturalnumber times as large as a size of the “small unit”.

The above relation between the units may be set as following example:the sector unit (first unit)<the “small unit”<the page unit (secondunit)<the “large unit”<the block unit (third unit).

In the second embodiment, a track unit is used as the “large unit”. Asize of the track unit is twice or larger natural number times as largeas a size of the page unit and a size of the block unit is twice orlarger natural number times as large as a size of the track unit.

According to using the track unit, the data management that uses thetrack management table and the track FIFO management table instead ofthe block management table is performed.

As with the first embodiment, in order to simplify the explanation, thepage unit is used as the “small unit”. However, a cluster unit may beused as the “small unit”. A size of the cluster unit is twice or lagernatural number times as large as a size of the sector unit and a size ofthe page unit is twice or larger natural number times as large as a sizethe cluster unit. The data management using the cluster unit isdescribed later.

A first memory area 11 temporarily stores data from a host apparatus.The data is written by the sector unit (the first unit) or less in thefirst memory area 11. The first memory area 11 is included in a volatilesemiconductor memory such as a DRAM.

A second memory area 12 is composed of blocks in a nonvolatilesemiconductor memory 22. In the nonvolatile semiconductor memory 22, theunit in which reading/writing is executed at one time is a page (thesecond unit) and the unit in which erasing is executed at one time is ablock (the third unit). A size of the block unit is natural number timesas large as a size of the page unit. The second memory area 12 storesdata by the “small unit” which is equal to the page unit.

A third memory area 13 is composed of blocks in the nonvolatilesemiconductor memory 22 and stores data by the “large unit” which isequal to the track unit.

A fourth memory area 14 is composed of blocks in the nonvolatilesemiconductor memory 22 and stores data by the “small unit” which isequal to the page unit.

A fifth memory area 15 is composed of blocks in the nonvolatilesemiconductor memory 22 and stores data by the “large unit” which isequal to the track unit.

The storage capacity of the first memory area 11 is assumed to be largerthan a size of the one block unit in the nonvolatile semiconductormemory 22, and the storage capacity of the nonvolatile semiconductormemory 22 is assumed to be larger than the storage capacity provided asthe product specification of the semiconductor storage device (forexample, SSD).

The storage capacity of the nonvolatile semiconductor memory 22 isallocated to the second, third, fourth, and fifth memory areas 12, 13,14, and 15 as follows.

The storage capacity is allocated to the third and fifth memory areas 13and 15 so that the total of the storage capacities of the third andfifth memory areas 13 and 15 is larger than the storage capacityprovided as the product specification of the semiconductor storagedevice (for example, the capacity larger by about 1 to 5% than thestorage capacity provided as the product specification of thesemiconductor storage device is allocated).

Although the rate of the capacity between the third and fifth memoryareas 13 and 15 is not limited, for example, the storage capacity of thethird memory area 13 is set to be the same as the storage capacityprovided as the product specification of the semiconductor storagedevice, and the storage capacity of the fifth memory area 15 is set tobe about 1 to 5% of the storage capacity of the third memory area 13.

The storage capacity remaining by subtracting the storage capacities ofthe third and fifth memory areas 13 and 15 from the storage capacity ofthe nonvolatile semiconductor memory 22 is allocated to the second andfourth memory areas 12 and 14. Each storage capacity of the second andfourth memory areas 12 and 14 and the rate between them are not limited.

The second, third, fourth, and fifth memory areas 12, 13, 14 and 15 arecomposed of, for example, one or more blocks in the nonvolatilesemiconductor memory 22, such as a NAND type flash memory.

In the second embodiment, in addition to the first, second, third, andfourth memory areas 11, 12, 13, and 14 described in the firstembodiment, the fifth memory area is provided by allocating one or moreblock thereto.

As in the first embodiment, the first, second, and third unitsrepresenting a size of data do not include redundant data (ECC, internalcontrol flag, etc.) which is added to main data from the host apparatusin the semiconductor storage device.

The controller 10 operates a program for executing data management. Thefunctions realized by the controller 10 can be implemented as any ofhardware and software or the combination of the both. Whether thesefunctions are implemented as hardware or software depends on thepractical embodiment or the design constraints imposed on the entiresystem.

When the main memory of the controller 10 is comprised of a volatilesemiconductor memory such as DRAM, the first memory area 11 may beconfigured in the main memory of the controller 10.

The controller 10 includes a cache management table, a page managementtable, a track management table, a page FIFO management table, a trackFIFO management table, and a physical block management table in order tomanage where data accessed by the logical address from the hostapparatus is stored in the first, second, third, fourth, and fifthmemory areas 11, 12, 13, 14, and 15.

——Cache Management Table——

The cache management table of FIG. 30 controls data stored in the firstmemory area 11 by the “small unit” which is equal to the page unit. Thecontrol of valid data is executed by the sector unit.

The configuration of the cache management table is shown in FIG. 21, asin the first embodiment. Since the cache management table has alreadybeen described in the first embodiment, the description is omitted here.

——Page Management Table——

The page management table of FIG. 30 controls data stored in the secondand fourth memory areas 12 and 14 by the “small unit” which is equal tothe page unit.

The configuration of the page management table is shown in FIG. 22, asin the first embodiment. Since the page management table has alreadybeen described in the first embodiment, the description is omitted here.

——Track Management Table——

FIG. 31 shows an example of a track management table.

The track management table controls data stored in the third and fifthmemory areas 13 and 15 by the “large unit” which is equal to the trackunit.

It is assumed that one entry is assigned to one block in the third andfifth memory areas 13 and 15.

The number of entries is assumed to be provided with allowance, in orderto register the blocks in processing, to the number of blocks which canbe contained within the third and fifth memory areas 13 and 15, that is,the number providing an allowance to [(the total capacity of the thirdand fifth memory areas 13 and 15)/(a size of the block unit)].

The physical address of the block allocated to the third memory area 13or the fifth memory area 15 is associated with each entry, and thelogical addresses of track unit data in the block are recorded in eachentry.

A page availability is configured to be able to distinguish“write-enable” state (this storage area is empty) from “write-inhibit”state (this storage area is invalid because old data has once writtentherein and new data is written in another storage area) for pages inthe area of the track unit.

In this example, the entry is configured by the block unit; however, inorder to search the physical address of the block at high speed, fromthe logical address of the data, the entry of the track management tablemay be configured by the track unit arranged in order of the logicaladdresses.

——Page FIFO Management Table——

The page FIFO management table of FIG. 30 controls data in the blocksallocated to the fourth memory area 14.

The configuration of the page FIFO management table is shown in FIG. 24,as in the first embodiment. Since the page FIFO management table hasalready been described in the first embodiment, the description isomitted here.

——Track FIFO Management Table——

FIG. 32 shows an example of a track FIFO management table.

The track FIFO management table controls data in the blocks allocated tothe fifth memory area 15.

It is assumed that one entry is assigned to one block in the fifthmemory area 15. The number of entries is assumed to be the number ofblocks which can be allocated to the fifth memory area 15, that is, (thetotal capacity of the fifth memory area 15)/(a size of the block unit).

The fifth memory area 15 is managed with FIFO (First-In First-Out)structure of the block unit by using the track FIFO management table.

An entry corresponding to a block newly allocated (inputted) to thefifth memory area 15 is added to the top (the entrance side) of thetrack FIFO management table, and entries originally registered in thetrack FIFO management table are shifted backward one by one.

When the number of entries exceeds a permissive range, the block havingthe oldest allocation order associated with the entry at the bottom (theexit side) of the track FIFO management table is outputted from thefifth memory area 15.

——Physical Block Management Table——

FIG. 33 shows an example of the physical block management table.

The physical block management table controls the usage of the blocks inthe nonvolatile semiconductor memory 22.

It is assumed that one entry is assigned to one block (physical block)in the second, third, fourth, and fifth memory area 12, 13, and 14. Thenumber of entries is assumed to be the number of blocks which can beused as a data area. Each entry is associated with the physical addressof the block and stores the usage of the block (whether the storage area(block) is used as the second, third, fourth, and fifth memory areas(active) or is unused (free)).

A processing flow executed by the controller 10 of FIG. 30 is described.

The data stored in the first memory area 11 classified into the “smallunit” or the “large unit”, and the “small unit” data is outputted to thefourth memory area 14. The operation of the FIFO process in the fourthmemory area 14 is the same as the first embodiment.

Namely, the FIFO process in the fourth memory area 14 is the same as theflow of FIG. 26. The process applied for the block which overflows fromthe fourth memory area 14 is substantially the same as the flow of FIG.27 (however, the destination of the “large unit” data is the fifthmemory area 15).

According to this configuration, as shown in the flows of FIG. 28 or 29,a target to be subjected to the compaction in the second memory area 12is data having a low updating frequency outputted from the fourth memoryarea 14. Therefore, the erasing count is reduced to prevent thedeterioration of memory cells.

However, in the second embodiment, the data which is determined to beoutputted as “large unit” data from the first memory area 11 and thedata which is determined to be outputted as “large unit” data from thesecond and fourth memory areas 12 and 14 are divided into data having ahigh updating frequency and data having a low updating frequency. Thetechnique that only for the data having a low updating frequency is, inprinciple, a target to be subjected to the compaction is described.

In this embodiment, the track unit which has smaller size than the blockunit is used as the “large unit”, and the data management in the thirdand fifth memory areas 13 and 15 is performed in the track unit. Namely,a size of the management unit is smaller than a size of the block unit(the minimum erase unit) in the third and fifth memory areas 13 and 15,and therefore, the invalid data is generated in the blocks, whereby thecompaction process is required to be performed.

Here, the data having a high updating frequency and the data having alow updating frequency are discriminated from each other, and in orderto improve the efficiency of the compaction, the fifth memory area 15having FIFO structure of the block unit is disposed before the thirdmemory area 13.

The following operation will be described. The data which is determinedto be outputted as “large unit” data from the first memory area 11 andthe data which is determined to be outputted as “large unit” data fromthe second and fourth memory areas 12 and 14 are subjected to the FIFOprocess in the fifth memory area 15.

A. FIFO Process in the Fifth Memory Area

FIG. 34 shows FIFO process in the fifth memory area 15. To simplify theexplanation, the data which is determined to be outputted as “largeunit” data from the first memory area 11 is particularly considered.

1. The controller 10 refers to entries of the track management tablecorresponding to a block prepared for writing data in appending manner(hereinafter referred to as a physical block for track-append). Thecontroller 10 stores data outputted from the first memory areas 11 asdata of the “large unit” which is equal to the track unit, in an area ofthe track unit with write-enable state in the physical block fortrack-append (Step ST1).

The controller 10 searches the cache management table and judges whetherall of sector unit data composing track unit data, which are determinedto be outputted, exist in the first memory area 11.

If not all sector unit data are completed in the first memory area 11,the controller 10 collects missing data from the second, third, fourth,and fifth memory areas 12, 13, 14, and 15.

After completing all sector unit data composing track unit data, thecontroller 10 instructs the nonvolatile semiconductor memory 22 to writethe track unit data in the physical block for track-append.

2. The controller 10 updates the logical address, recorded in the entrycorresponding to the area of the track unit (pages) in which the trackunit data has been written, in the track management table (Step ST2).The old data included in the same logical address range, which had beenwritten in the second, third, fourth, and fifth memory areas 12, 13, 14,and 15 becomes invalid data.

3. The controller 10 judges whether there exits an empty area of thetrack unit (empty pages) in the physical block for track-append (StepST3). If the empty pages are not detected, this process goes to the stepST4. If the empty pages are detected, this process returns to the stepST1.

4. The controller 10 shifts the entries of the track FIFO managementtable backward one by one, and adds the physical address of the physicalblock for track-append to the entry at the top of the track FIFOmanagement table (Step ST4). As a result, the physical block fortrack-append is allocated to the fifth memory area 15.

5. The controller 10 updates the entry corresponding to a block, whichoverflows from the fifth memory area 15, to be “third memory area 13(active)” in the physical block management table (Step ST5).

In the data transfer from the fifth memory area 15 to the third memoryarea 13, the controller only updating the track FIFO management tableand the physical block management table without instructing thenonvolatile semiconductor memory 22 to read/write data (Move process).

B. Process Example 1

FIG. 35 shows the flowchart of process example 1.

1. The controller 10 gets a free block by searching the physical blockmanagement table. After erasing data in the free block, this block isallocated to a compaction block. The controller 10 searches an unusedentry in the track management table. The physical address of thecompaction block is associated with the unused entry (Step ST1).

2. The controller 10 sequentially selects valid data of the track unitin order from the block with the smallest number of valid data byscanning the track management table. The selected valid data is copiedto the compaction block and the logical addresses in the entry of thetrack management table associated with the compaction block are updatedto the logical addresses of the copied data (Step ST2).

In the scanning of the track management table, the entries associatedwith the physical addresses included in the track FIFO management tableand the entry corresponding to the physical block for track-append arenot scanned. Namely, the third memory area 13 is scanned, but the fifthmemory area 15 is not scanned.

At the step ST2 (the compaction), the valid data included in the logicaladdress range of the copied data may be read out from the first, second,and fourth memory areas 11, 12, and 14 and the copied data may beoverwritten with the valid data. The valid data in the first, second,and fourth memory areas 11, 12, and 14 involved in the compaction isrendered invalid state.

3. If all the data in a block becomes invalid data, the controller 10releases the block and sets the status of the block to be “free” statefrom “active” state in the physical block management table (Step ST3).

4. The controller 10 judges whether the number of blocks in the thirdmemory area 13 is the predetermined number of blocks defined as thecapacity of the third memory area 13 or less (Step ST4).

If the number of blocks in the third memory area 13 is the predeterminednumber of blocks defined as the capacity of the third memory area 13 orless, this process is completed. If the number of blocks in the thirdmemory area 13 is larger than the predetermined number of blocks definedas the capacity of the third memory area 13, this process returns to thestep ST1.

C. Process Example 2

The compaction might not be able to be performed simply by using theblocks in the third memory area 13. Specifically, when the storagecapacity as the product specification of the semiconductor storagedevice is larger than the storage capacity of the third memory area 13and smaller than the total storage capacity of the third and fifthmemory areas 13 and 15, the compaction might not be able to beperformed.

Such a situation may occurs due to demand that the capacity as theproduct specification is made as close as possible to the total capacityof the NAND type flash memories in the semiconductor storage device.

In this case, when the total size (storage capacity) of the invalid dataexisting in the third memory area 13 does not reach a size of the blockunit, a free block cannot be newly generated no matter how many timesthe compaction is performed in the third memory area 13.

Thus, in the above situation, the compaction is applied to both thethird memory area 13 and the fifth memory area 15 only on an exceptionalbasis (the fifth condition).

FIG. 36 shows the flowchart of process example 2.

1. The controller 10 gets a free block by searching the physical blockmanagement table. After erasing data in the free block, this block isallocated a compaction block. The controller 10 searches an unused entryin the track management table. The physical address of the compactionblock is associated with the unused entry (Step ST1).

2. The controller 10 sequentially selects valid data of the track unitin order from the block with the smallest number of valid data byscanning the track management table. The selected valid data is copiedto the compaction block and the logical addresses in the entry of thetrack management table associated with the compaction block are updatedto the logical addresses of the copied data (Step ST2).

In the scanning of the track management table, the entries associatedwith the physical addresses included in the track FIFO management tableare also scanned. Namely, the third memory area 13 and the fifth memoryarea 15 are scanned.

At the step ST2 (the compaction), the valid data included in the logicaladdress range of the copied data may be read out from the first, second,and fourth memory areas 11, 12, and 14 and the copied data may beoverwritten with the valid data. The valid data in the first, second,and fourth memory areas 11, 12, and 14 involved in the compaction isrendered invalid state.

3. If all the data in a block becomes invalid data, the controller 10releases the block and sets the status of the block to be “free” statefrom “active” state in the physical block management table (Step ST3).

4. The controller 10 adds the compaction block to the top of the trackFIFO management table (Step ST4). This is because the invalid data inthe fifth memory area 15 is required to be reduced.

If the number of invalid data in the fifth memory area 15 is reduced,the number of invalid data in the third memory area 13 is increased.Therefore, the compaction is applied only to the third memory area 13 asshown in the above process example 1, whereby the valid data in thethird memory area 13 are collected, and a free block can be generated inthe third memory area 13.

5. The controller 10 judges whether the number of blocks in the thirdand fifth memory areas 13 and 15 is the predetermined number of blocksdefined as the capacity of the third and fifth memory areas 13 and 15 orless (Step ST5).

If the number of blocks in the third and fifth memory areas 13 and 15 isthe predetermined number of blocks defined as the capacity of the thirdand fifth memory areas 13 and 15 or less, this process is completed. Ifthe number of blocks in the third and fifth memory areas 13 and 15 islarger than the predetermined number of blocks defined as the capacityof the third and fifth memory areas 13 and 15, this process returns tothe step ST1.

In each step ST1 in the process examples 1 and 2, as the process example2 in the first embodiment (FIG. 29), two or more blocks with thesmallest number of valid data of the track unit may be selected and thevalid data may be copied to the compaction block.

In the second embodiment, the controller 10 allocates the storage area(the blocks) to the second memory area 12, the third memory area 13, thefourth memory area 14, and the fifth memory area 15, whereby the datamanagement in the nonvolatile semiconductor memory is performed.However, it is not limited to this.

For example, the data management may be performed by configuring thesecond memory area 12, the third memory area 13, and the fifth memoryarea 15 without configuring the fourth memory area 14. Otherwise, thedata management may be performed by configuring the third memory area 13and the fifth memory area 15 without configuring the second memory area12 and the fourth memory area 14.

(3) Third Embodiment

A third embodiment relates to data management configuration in thesecond and fourth memory areas 12 and 14, for reducing theimplementation cost and the verification cost.

FIG. 37 shows a semiconductor storage device according to the thirdembodiment.

A first memory area 11 temporarily stores data from a host apparatus.The data is written by the sector unit (the first unit) or less in thefirst memory area 11. The first memory area 11 is included in a volatilesemiconductor memory such as a DRAM.

A second memory area 12 is composed of blocks in a nonvolatilesemiconductor memory 22. In the nonvolatile semiconductor memory 22, theunit in which reading/writing is executed at one time is a page (thesecond unit) and the unit in which erasing is executed at one time is ablock (the third unit). A size of the block unit is a natural numbertimes as large as a size of the page unit. The second memory area 12stores data by the “small unit” which is equal to the page unit.

A third memory area 13 is composed of blocks in the nonvolatilesemiconductor memory 22 and stores data by the “large unit” which isequal to the block unit.

A fourth memory area 14 is composed of blocks in the nonvolatilesemiconductor memory 22 and stores data by the “small unit” which isequal to the page unit.

The storage capacity of the first memory area 11 is assumed to be largerthan a size of the one block unit in the nonvolatile semiconductormemory 22, and the storage capacity of the nonvolatile semiconductormemory 22 is assumed to be larger than the storage capacity provided asthe product specification of the semiconductor storage device (forexample, SSD).

The storage capacity of the nonvolatile semiconductor memory 22 isallocated to the second, third, and fourth memory areas 12, 13, and 14as follows.

The storage capacity, which is the same as or larger than the storagecapacity provided as the product specification of the semiconductorstorage device, is allocated to the third memory area 13.

The storage capacity remaining by subtracting the storage capacity ofthe third memory area 13 from the storage capacity of the nonvolatilesemiconductor memory 22 is allocated to the second and fourth memoryareas 12 and 14. Each storage capacity of the second and fourth memoryareas 12 and 14 and the rate are not limited.

The second, third, and fourth memory areas 12, 13, and 14 are composedof, for example, one or more blocks in the nonvolatile semiconductormemory 22, such as a NAND type flash memory.

The first, second, and third units representing a size of data do notinclude redundant data (ECC, internal control flag, etc.) which is addedto main data from the host apparatus in the semiconductor storagedevice.

A controller 10 has a CPU and a main memory, and can operate a programfor executing data management. In this embodiment, the functionsrealized by the controller 10 can be implemented as any of hardware andsoftware or the combination of the both. Whether these functions areimplemented as hardware or software depends on the practical embodimentor the design constraints imposed on the entire system.

When the main memory of the controller 10 is comprised of a volatilesemiconductor memory such as DRAM, the first memory area 11 may beconfigured in the main memory of the controller 10.

The controller 10 includes a cache management table, a page managementtable, a block management table, a page FIFO management table, and aphysical block management table in order to manage where data accessedby the logical address from the host apparatus is stored in the first,second, third and fourth memory areas 11, 12, 13, and 14. Thesemanagement tables are expanded onto the main memory of the controller 10during the operation of the semiconductor storage device.

——Cache Management Table——

The cache management table of FIG. 37 controls data stored in the firstmemory area 11 by the “small unit” which is equal to the page unit. Thecontrol of the valid data is executed by the sector unit.

The configuration of the cache management table is shown in FIG. 21 asin the first embodiment. Since the cache management table has alreadybeen described in the first embodiment, the detailed description isomitted here.

——Page Management Table——

The page management table of FIG. 37 controls data stored in the secondand fourth memory areas 12 and 14 by the “small unit” which is equal tothe page unit.

The configuration of the page management table is shown in FIG. 22 as inthe first embodiment. Since the page management table has already beendescribed in the first embodiment, the detailed description is omittedhere.

——Block Management Table——

The block management table of FIG. 37 controls data stored in the thirdmemory area 13 by the “large unit” which is equal to the block unit.

The configuration of the block management table is shown in FIG. 23 asin the first embodiment. Since the block management table has alreadybeen described in the first embodiment, the detailed description isomitted here.

——Page FIFO Management Table——

The page FIFO management table of FIG. 37 controls data in the blocksallocated to the fourth memory area 14.

The configuration of the page FIFO management table is shown in FIG. 24as in the first embodiment. Since the page FIFO management table hasalready been described in the first embodiment, the detailed descriptionis omitted here.

——Physical Block Management Table——

The physical block management table of FIG. 37 controls the usage ofblocks in the nonvolatile semiconductor memory 22.

The configuration of the physical block management table is shown inFIG. 25 as in the first embodiment. Since the physical block managementtable has already been described in the first embodiment, the detaileddescription is omitted here.

A process flow executed by the controller 10 of FIG. 37 is described.

The controller 10 first writes sector unit (first unit) data from thehost apparatus in the first memory area 11 and stores the data for acertain period therein. With regard to this data store process, “A. Datastore process in the first memory area” described in the section I. canbe applicable.

The controller 10 distinguishes whether the data stored in the firstmemory area 11 should be managed with the “small unit (first managementunit)” or the “large unit (second management unit)”, based on apredetermined condition (which may be substantially the same as thefirst condition of “B. Data output process from the first memory area”described in the section I.).

A size of the “small unit” is a natural number times as large as a sizeof the page unit or a size of the page unit is a natural number times aslarge as a size of the “small unit”.

A size of the “large unit” is twice or larger natural number times aslarge as a size of the “small unit”, and at the same time, is a naturalnumber times as large as a size of the block unit.

In this embodiment, to simplify the explanation, each of the units usedin management tables is assumed below:

A size of the “small unit” which is a data management unit in the secondand fourth memory areas 12 and 14 is equal to a size of the page unit(second unit). A size of the “large unit” which is a data managementunit in the third memory area 13 is equal to a size of the block unit(third unit).

However, a page is controlled by being divided, specifically, a size ofthe “small unit” may be a natural number times as large as a size of thesector unit and a size of the page unit may be twice or larger naturalnumber times as large as a size of the “small unit”.

Alternatively, plural pages are collectively controlled, specifically, asize of the “small unit” may be twice or larger natural number times aslarge as a size of the page unit and a size of the block unit may betwice or larger natural number times as large as a size of the “smallunit”.

Likewise, a block is controlled by being divided, specifically, a sizeof the “large unit” may be twice or larger natural number times as largeas a size of the “small unit” and a size of the block unit may be twiceor larger natural number times as large as a size of the “large unit”.

Alternatively, plural blocks are collectively controlled, specifically,a size of the “large unit” may be twice or larger natural number timesas large as a size of the block unit.

The above relation between the units may be set as following example:the sector unit (first unit)<the “small unit”<the page unit (secondunit)<the block unit (third unit) the “large unit”.

If the data stored in the first memory area 11 is managed with the“small unit”, the data is transferred to the fourth memory area 14. Ifthe data stored in the first memory area 11 is managed with the “largeunit”, the data is transferred to the third memory area 13.

This data output process is substantially the same as “B. Data outputprocess from the first memory area” described in the section I. However,different from the section I., the destination of the “small unit” datais the fourth memory area 14.

A. FIFO Process in the Fourth Memory Area

As already described, the fourth memory area 14 has the FIFO structureof the block unit. FIG. 38 shows the FIFO process in the fourth memoryarea 14.

1. The controller 10 refers to entries of the page management tablecorresponding to a block prepared for writing data in appending manner(hereinafter referred to as a physical block for page-append). Thecontroller 10 stores data outputted from the first memory area 11, asdata of the “small unit” which is equal to the page unit, in a page ofwrite-enable state of the physical block for page-append (Step ST1).

2. The controller 10 updates the logical address, recorded in the entrycorresponding to the page in which the page unit data has been written,in the page management table (Step ST2). The old data included in thesame logical address range, which had been written in the second andfourth memory areas 12 and 14, becomes invalid data.

3. The controller 10 judges whether there exits an empty page in thephysical block for page-append (Step ST3). If the empty page is notdetected, this process goes to the step ST4. If the empty page isdetected, this process returns to the step ST1.

4. The controller 10 shifts the entries of the page FIFO managementtable backward one by one, and adds the physical address of the physicalblock for page-append to the entry at the top of the page FIFOmanagement table (Step ST4). As a result, the physical block forpage-append is allocated to the fourth memory area 14.

5. The controller 10 executes the following process P1 for all theblocks in the fourth memory area 14 of which physical addresses arerecorded in the page FIFO management table (Step ST5).

The process P1 is different from the first embodiment and the secondembodiment in the point of adopting the compaction. This point iseffective in the case where the utilization efficiency of blocks in thefourth memory area 14 is bad. In order to suppress the increase ofwriting operation, the block with much valid data is excluded from theobject of the compaction.

B. Process P1

FIG. 39 shows the flowchart of process P1. FIG. 40 shows the state ofthe blocks in the fourth memory area 14 during executing the process P1.Each of the blocks is composed of plural pages. Each of the pages isrendered to be any of three states including “valid”, “invalid”, and“empty” by referring page availability in the page management table.

1. The controller 10 counts up the number of valid data stored in eachblock, with respect to all the blocks in the fourth memory area 14, bysearching the page management table at the physical addresses recordedin the page FIFO management table (Step ST1).

2. The controller 10 judges whether there exits a block in which thenumber of valid data counted at the step ST1 is a predeterminedthreshold value or more. For example, the predetermined threshold valuemay be set to be 50% of the total number of page unit (“small unit”)data storable in one block (Step ST2).

If the block, in which the number of valid data is the predeterminedthreshold value or more, is detected, this process goes to the step ST3.If the block is not detected, this process goes to the step ST4.

3. The controller 10 moves the blocks, in which the number of valid datais the predetermined threshold value or more, to the second memory area12 (Step ST3). That is, with respect to the physical address of theblock, the controller 10 invalidates the entry of the page FIFOmanagement table and updates the entry of the physical block managementtable to be “second memory area (active)”.

In the data transfer from the fourth memory area 14 to the second memoryarea 12, the controller only updating the page FIFO management table andthe physical block management table without instructing the nonvolatilesemiconductor memory 22 to read/write data (Move process).

4. The controller 10 sequentially selects valid data in order from theblock with the oldest allocation order in the fourth memory area 14. Theselected valid data is copied to an erased free block (compactionblock). The controller 10 allocates the compaction block filled withvalid data to the second memory area 12 (Step ST4).

5. The controller 10 invalidates the data, which has the same logicaladdress as the copied data, in the fourth memory area 14. If all thedata in a block becomes invalid data, the controller 10 releases theblock and sets the status of the block to be “free” state from “active”state in the physical block management table (Step ST5).

If there exits no empty page in the physical block for page-append, thecontroller 10 gets a free block by searching the physical blockmanagement table. After erasing data in the free block, this block isnewly allocated to a physical block for page-append. The controller 10searches an unused entry in the page management table. The physicaladdress corresponding to the physical block for page-append is recordedin the unused entry.

According to the movement of the blocks from the fourth memory area 14,the number of blocks managed with the page unit is increased in thesecond memory area 12. If the number of blocks in the second memory area12 exceeds a permissive range, that is, the predetermined number ofblocks defined as the capacity of the second memory area 12, thecontroller 10 executes the compaction or the data transfer process fromthe second memory area 12 to the third memory area 13 by the followingprocedures.

In addition, different from the first embodiment, the process P1 doesnot include the data transfer process (Defragmentation) to the thirdmemory area 13. This simplifies the data transfer process from thefourth memory area 14 to the second memory area 12.

C. Process Example

FIG. 41 shows the flowchart of process example. FIGS. 42 to 46 show thestate of the blocks in the second memory area 12 during executing theprocess of FIG. 41. As illustrated in FIGS. 42 to 46, the allocationorder of the blocks in the second memory area 12 is managed by thecontroller 10.

Each of the blocks is composed of plural pages. Each of the pages isrendered to be any of three states including “valid”, “invalid”, and“empty” by referring to page availability in the page management table.

1. According to the above process P1, the controller 10 transfers datafrom the fourth memory area 14 to the second memory area 12 (Step ST1).

2. The controller 10 judges whether the number of blocks in the secondmemory area 12 exceeds a permissive range (Step ST2). The permissiverange may be the predetermined number of blocks defined as the capacityof the second memory area 12.

If the number of blocks does not exceed the permissive range, thisprocess is completed. If the number of blocks exceeds the permissiverange, this process goes to the step ST3.

3. The controller 10 counts up the number of valid data (the number ofentries) stored in a specified range of the blocks by referring to thepage management table and judges whether the total number of valid datastored in the specified range is larger than a predetermined thresholdvalue (Step ST3).

The specified range includes two adjacent blocks in the second memoryarea 12, for example. “Adjacent blocks” means the blocks of whichallocation order is successive. A “window” of FIG. 42 shows thespecified range of the blocks. A starting position of the “window” isset so as to include the block with the oldest allocation order.

The predetermined threshold value at the step ST3 may be the number ofpage unit data storable in the half of the blocks included in thespecified range. FIG. 42 shows the two blocks included in the specifiedrange, and the predetermined number is set to be the number of page unitdata storable in one block which is the half of the two blocks.

If the number of valid data is larger than the predetermined thresholdvalue, this process goes to the step ST4. If the number of valid data isthe predetermined threshold value or less, this process goes to the stepST7 and the controller 10 executes the defragmentation and thecompaction (FIGS. 43 and 44) for the present “window”.

4. The controller 10 shifts the “window” from older side to the newerside (Step ST4). Specifically, the controller 10 shifts the “window” oneby one from the side of the block with the oldest allocation order tothe block with the newest allocation order, in the second memory area12.

5. The controller 10 judges whether the “window” has exceeded the blockwith the newest allocation order in the second memory area 12 (StepST5). If the “window” has exceeded the block with the newest allocationorder, this process goes to the step ST6. If the “window” has notexceeded the block with the newest allocation order, this processreturns to the step ST3.

6. The controller 10 selects all valid data in the block with the oldestallocation order and transfers the selected valid data to the thirdmemory area 13 as data of the “large unit” which is equal to the blockunit (Defragmentation) (Step ST6). The step ST6 is executed in the casewhere the controller 10 cannot detect the target of the compaction inthe second memory area 12.

As shown in FIG. 45, valid data included in the logical address range,which is calculated by aligning the logical address of the valid datastored in the block with the oldest allocation order by a size of theblock unit (“large unit”), are collected from the first, second, third,and fourth memory areas 11, 12, 13, and 14.

The controller 10 instructs the nonvolatile semiconductor memory 22 towrite the block unit data in the third memory area 13. After writing theblock unit data, the controller 10 releases the block with oldestallocation order, and this process returns to the step ST2. A positionof the “window” is reset to the starting position.

7. The controller 10 searches the physical block management table andgets free blocks (compaction blocks) (Step ST7). The free blocks areprovided for the compaction and the number of free blocks required atthe step ST7 is the half of the blocks included in the specified range.In FIG. 44, one free block is provided for the compaction. Thecontroller 10 instructs the nonvolatile semiconductor memory 22 to erasedata in the free blocks.

8. The controller 10 sequentially selects valid data stored in the“window” (Step ST8). If all valid data stored in the “window” has beenprocessed, the blocks positioned at newer side than that of the “window”are further searched in order of allocation to the fourth memory area14, and the controller 10 continues to select valid data.

9. The controller 10 judges whether the total number of valid dataincluded in the logical address range, which is calculated by aligningthe logical address of the selected valid data by a size of the blockunit (“large unit”), is a predetermined threshold value or more in thesecond and fourth memory areas 12 and 14 (Step ST9). The predeterminedthreshold value at the step ST9 may be set to be 500 of the total numberof page unit (“small unit”) data storable in one area of the block unit(“large unit”).

If the total number of valid data is less than the predeterminedthreshold value, this process goes to the step ST10. If the total numberof valid data is the predetermined threshold value or more, this processgoes to the step ST11.

10. The controller 10 copies (rewrites) the selected valid data to thecompaction blocks, as shown in FIG. 44 (Step ST10). The logical addressof the copied valid data is newly recorded on the entry associated withthe compaction block in the page management table. The logical addressof the copied valid data originally recorded on the entry associatedwith the blocks allocated to the second memory area 12 is set to beinvalid state in the page management table.

11. The controller 10 collects valid data included in the logicaladdress range aligned by a size of the block unit (“large unit”) fromthe first, second, third, and fourth memory areas 11, 12, 13, and 14, asshown in FIG. 43, and transfers the selected valid data to the thirdmemory area 13 as data of the “large unit” which is equal to the blockunit (Defragmentation) (Step ST11).

12. The controller 10 releases the block in which all of data isrendered invalid according to the compaction at the step ST10 or thedefragmentation at the step ST11 (Step ST12). The controller 10 sets thestatus of the block to be “free” state from “active” state in thephysical block management table, as shown in FIG. 46.

13. The controller 10 judges whether the compaction block is filed withvalid data of the page unit (Step ST13). If the compaction block is notfiled with valid data, this process returns to the step ST8. If thecompaction block is filed with valid data, this process goes to the stepST14.

However, in the case where the compaction block cannot be filled withvalid data even if all valid data is selected at the step ST8, thisprocess goes to the step ST 14. In this case, the compaction blockhaving empty pages therein may be allocated to the second memory area12.

14. The controller 10 inserts the compaction block immediately beforethe “window” in the second memory area 12, as shown in FIG. 44. That is,the compaction block is inserted on the older side than the “window”,whereby the block newly allocated to the second memory area 12 isprevented from being subject to the target of the compaction again.

After updating the page management table and the physical blockmanagement table, this process returns to the step ST2. When thisprocess returns to the step ST2 and new compaction process is triggered,a position of the “window” is kept at the present position, as shown inFIG. 46.

In the present process example, the controller 10 judges whether or notthe compaction is applicable, only for the specified range (“window”),whereby the searching process to detect the target of the compaction canbe simplified and the implementation cost and the verification cost canbe reduced.

The number of blocks included in the specified range is not limited tothe two. The controller 10 may defines the three or more blocks as thespecified range. The controller 10 may judge whether valid data storedin the specified range is larger than the number of page unit datastorable in the blocks decreased by one from the number of the blocksincluded in the specified range.

3. Application Example

The semiconductor storage device according to the above embodiments canbe applied to an SSD (Solid State Drive) used as a secondary storagedevice for a personal computer such as a notebook computer. The specificexample in this case is described below.

4. Conclusion

The semiconductor storage device according to the first, second, andthird embodiments subjects the data having a low updating frequency tothe compaction process, whereby reduces the erasing count of the blocksin the nonvolatile semiconductor memory. In addition, the semiconductorstorage device uses two data management units; the “large unit” and the“small unit” as described in the section I., whereby realizes theimprovement of the writing efficiency.

The present invention is not limited to the above-described embodiments,and the components can be modified and embodied without departing fromthe spirit and scope of the invention. Further, the suitable combinationof the plurality of components disclosed in the above-describedembodiments can form various inventions. For example, several componentsmay be omitted from all the components disclosed in the aboveembodiments. Still further, the components over the differentembodiments may be suitably combined with each other.

[III. Relation Between Data Management Units and Reading/Writing/ErasingUnits]

1. Outline

In the above description, the semiconductor storage device according tothe section I. and the section II. are respectively described. In thissection, the first, second, and third units and the “small unit” and the“large unit” used in the above description will be specificallydescribed.

The first unit is specified as data input and/or output unit withrespect to a volatile or nonvolatile semiconductor memory which includesthe first memory area 11. The first memory area 11 performsreading/writing of data by the first unit or less. The first unit may bea sector unit, for example. The host apparatus, such as a personalcomputer, executes an access to the semiconductor storage device by thesector unit.

The second unit is specified as the minimum data reading and/or writingunit in a nonvolatile semiconductor memory which includes the second,third, fourth, and fifth memory areas 12, 13, 14, and 15.

The third unit is specified as the minimum data erasing unit in anonvolatile semiconductor memory which includes the second, third,fourth, and fifth memory areas 12, 13, 14, and 15.

If the second, third, fourth, and fifth memory areas 12, 13, 14, and 15are configured in a NAND type flash memory, the second unit may be apage unit, and the third unit may be a block unit.

The second and third units are physically specified as the datareading/writing/erasing unit with respect to the second, third, fourth,and fifth memory areas 12, 13, 14, and 15 configured in the nonvolatilesemiconductor memory.

On the other hand, the data management units (the “small unit” and the“large unit”) in the semiconductor storage device may correspond to thephysical reading/writing/erasing unit in the nonvolatile semiconductormemory, or may be different therefrom.

In the following embodiment, the “small unit” which is the datamanagement unit with respect to the second and fourth memory areas 12and 14 is the cluster unit. A size of the cluster unit is a naturalnumber times as large as a size of the sector unit, and a size of thepage unit is twice or larger natural number times as large as a size ofthe cluster unit. A size of the cluster unit may be equal to a size ofthe file management unit used in the file system of the host apparatus.

2. Embodiment

An embodiment of the invention will be described.

FIG. 47 shows a semiconductor storage device according to the embodimentof the present invention.

A first memory area 11 temporarily stores data from a host apparatus.The data is written by the sector unit (the first unit) or less in thefirst memory area 11. The first memory area 11 is configured in avolatile semiconductor memory such as a DRAM.

A second memory area 12 is composed of blocks in a nonvolatilesemiconductor memory 22. In the nonvolatile semiconductor memory 22, theunit in which reading/writing is executed at one time is a page (thesecond unit) and the unit in which erasing is executed at one time is ablock (the third unit). A size of the block unit is a natural numbertimes as large as a size of the page unit. The second memory area 12stores data by the “small unit” which is equal to the cluster unit.

A third memory area 13 is composed of blocks in the nonvolatilesemiconductor memory 22 and stores data by the “large unit” which isequal to the block unit.

A fourth memory area 14 is composed of blocks in the nonvolatilesemiconductor memory 22 and stores data by the “small unit” which isequal to the cluster unit.

The storage capacity of the first memory area 11 is assumed to be largerthan a size of the one block unit in the nonvolatile semiconductormemory 22, and the storage capacity of the nonvolatile semiconductormemory 22 is assumed to be larger than the storage capacity provided asthe product specification of the semiconductor storage device (forexample, SSD).

The storage capacity of the nonvolatile semiconductor memory 22 isallocated to the second, third, and fourth memory areas 12, 13, and 14as follows.

The storage capacity, which is the same as or larger than the storagecapacity provided as the product specification of the semiconductorstorage device, is allocated to the third memory area 13.

The storage capacity remaining by subtracting the storage capacity ofthe third memory area 13 from the storage capacity of the nonvolatilesemiconductor memory 22 is allocated to the second and fourth memoryareas 12 and 14. Each storage capacity of the second and fourth memoryareas 12 and 14 and the rate between them are not limited.

A controller 10 has a CPU and a main memory, and can operate a programfor executing data management. In this embodiment, the functionsrealized by the controller 10 can be implemented as any of hardware andsoftware or the combination of the both. Whether these functions areimplemented as hardware or software depends on the practical embodimentor the design constraints imposed on the entire system.

When the main memory of the controller 10 is comprised of a volatilesemiconductor memory such as DRAM, the first memory area 11 may beconfigured in the main memory of the controller 10.

The controller 10 includes a cache management table, a clustermanagement table, a block management table, a cluster FIFO managementtable, and a physical block management table in order to manage wheredata accessed by the logical address from the host apparatus is storedin the first, second, third and fourth memory areas 11, 12, 13, and 14.These management tables are expanded onto the main memory of thecontroller 10 during the operation of the semiconductor storage device.

——Cache Management Table——

The cache management table of FIG. 47 controls data stored in the firstmemory area 11 by the “small unit” which is equal to the cluster unit.The control of the valid data is executed by the sector unit.

The configuration of the cache management table is shown in FIG. 21, asin the first embodiment of the section II. However, in this embodiment,it is assumed that one entry is assigned to one area of the cluster unitin the first memory area 11.

The number of entries is assumed to be the number of cluster unit datawhich can be contained within the first memory area 11, that is, notlarger than (the capacity of the first memory area 11)/(a size of thecluster unit).

A logical address of cluster unit data, a physical address of the firstmemory area 11, and a sector flag indicating the location of valid datain the relevant area of the cluster unit are associated with each entry.

——Cluster Management Table——

The cluster management table of FIG. 47 controls data stored in thesecond and fourth memory areas 12 and 14 by the “small unit” which isequal to the cluster unit. A size of the cluster unit is a naturalnumber times as large as a size of the sector unit, and a size of thepage unit is twice or larger natural number times as large as a size ofthe cluster unit.

FIG. 48 shows an example of the cluster management table.

It is assumed that one entry is assigned to one block in the second andfourth memory areas 12 and 14.

The number of entries is assumed to be provided with allowance, in orderto register the blocks in processing, to the number of blocks which canbe contained within the second and fourth memory areas 12 and 14, thatis, the number providing an allowance to [(the total capacity of thesecond and fourth memory areas 12 and 14)/(a size of the block unit)].

The physical address of the block allocated to the second memory area 12or the fourth memory area 14 is associated with each entry, and thelogical addresses of cluster unit data in the block are recorded in eachentry.

In FIG. 48, it is assumed that a size of the page unit is twice as largeas a size of the cluster unit. A cluster availability is configured tobe able to distinguish “write-enable” state (this storage area is empty)from “write-inhibit” state (this storage area is invalid because olddata has once written therein and new data is written in another storagearea) for each cluster.

In addition, in the case where cluster unit data which does not fulfillthe page boundary is written in the fourth memory area 14, the clusteravailability corresponding to the remaining area of the cluster unit inthe identical page is set to be “write-inhibit” state. Although theremaining area of the cluster unit does not store valid data, since thedata writing unit is the page unit and the nonvolatile semiconductormemory 22 cannot use the remaining area, the controller 10 treats theremaining area as invalid data.

——Block Management Table——

The block management table of FIG. 47 controls data stored in the thirdmemory area 13 by the “large unit” which is equal to the block unit. Theconfiguration of the block management table is shown in FIG. 23, as inthe first embodiment of the section II.

——Cluster FIFO Management Table——

The cluster FIFO management table of FIG. 47 controls data in the blocksallocated to the fourth memory area 14. The configuration of the clusterFIFO management table is shown in FIG. 24, as in the first embodiment ofthe section II.

——Physical Block Management Table——

The physical block management table of FIG. 47 controls the usage ofblocks in the nonvolatile semiconductor memory 22. The configuration ofthe physical block management table is shown in FIG. 25, as in the firstembodiment of the section II.

A process flow executed by the controller 10 of FIG. 47 is described.

The controller 10 first writes sector unit (first unit) data from thehost apparatus in the first memory area 11 and stores the data for acertain period therein. With regard to this data store process, “A. Datastore process in the first memory area” described in the section I. canbe applicable.

The controller 10 distinguishes whether the data stored in the firstmemory area 11 should be managed with the “small unit (first managementunit)” or the “large unit (second management unit)”, based on apredetermined condition (which may be substantially the same as thefirst condition of “B. Data output process from the first memory area”described in the section I.).

A size of the “small unit” is a natural number times as large as a sizeof the page unit or a size of the page unit is a natural number times aslarge as a size of the “small unit”.

A size of the “large unit” is twice or larger natural number times aslarge as a size of the “small unit”, and at the same time, is a naturalnumber times as large as a size of the block unit.

In this embodiment, a size of the “small unit” which is a datamanagement unit in the second and fourth memory areas 12 and 14 is twiceor larger natural number times as large as a size of the sector unit,and a size of the page unit is twice or larger natural number times aslarge as a size of the “small unit”. The “small unit” which satisfiesthis relation is called the cluster unit. To simplify the explanation, asize of the “large unit” which is a data management unit in the thirdmemory area 13 is equal to a size of the block unit.

The above relation between the units may be set as following example:the sector unit (first unit)<the cluster unit (“small unit”)<the pageunit (second unit)<the block unit (third unit)≦the “large unit”.

If the data stored in the first memory area 11 is managed with the“small unit”, the data is transferred to the fourth memory area 14. Ifthe data stored in the first memory area 11 is managed with the “largeunit”, the data is transferred to the third memory area 13.

This data output process is substantially the same as “B. Data outputprocess from the first memory area” described in the section I. However,different from the section I., the destination of the “small unit” datais the fourth memory area 14. Since a size of the cluster unit issmaller than a size of the page unit, a plurality of cluster unit datamay be involved and transferred to the fourth memory area 14.

A. FIFO Process in the Fourth Memory Area

As already described, the fourth memory area 14 has the FIFO structureof the block unit. FIG. 49 shows FIFO process in the fourth memory area14.

1. The controller 10 refers to entries of the cluster management tablecorresponding to a block prepared for writing data in appending manner(hereinafter referred to as a physical block for cluster-append). Thecontroller 10 stores data outputted from the first memory area 11, asdata of the “small unit” which is equal to the cluster unit, in an areaof the cluster unit with write-enable state in the physical block forcluster-append (Step ST1).

The controller 10 searches the cache management table and judges whetherall of sector unit data composing cluster unit data, which aredetermined to be outputted, exist in the first memory area 11.

If not all sector unit data are completed in the first memory area 11,the controller 10 collects missing data from the second, third, andfourth memory areas 12, 13, and 14.

After completing all sector unit data composing cluster unit data, thecontroller 10 instructs the nonvolatile semiconductor memory 22 to writethe cluster unit data. In the writing process at the step ST1, it ispreferable that a plurality of cluster unit data storable in theidentical page is written together.

2. The controller 10 updates the logical address, recorded in the entrycorresponding to the page in which the cluster unit data has beenwritten, in the cluster management table (Step ST2). The old dataincluded in the same logical address range, which had been written inthe second and fourth memory areas 12 and 14, becomes invalid data.

3. The controller 10 judges whether there exits an empty area of thecluster unit in the physical block for cluster-append (Step ST3). If theempty area of the cluster unit is not detected, this process goes to thestep ST4. If the empty area of the cluster unit is detected, thisprocess returns to the step ST1.

4. The controller 10 shifts the entries of the cluster FIFO managementtable backward one by one, and adds the physical address of the physicalblock for cluster-append to the entry at the top of the cluster FIFOmanagement table (Step ST4). As a result, the physical block forcluster-append is allocated to the fourth memory area 14.

5. The controller 10 executes the process P1 for all the blocks in thefourth memory area 14 of which physical addresses are recorded in thecluster FIFO management table (Step ST5).

The process P1 may be substantially the same as “B. Process P1” of FIG.39 described in the section II. However, valid data is managed with thecluster unit.

3. Conclusion

The data management units (the “small unit” and the “large unit”) in thesemiconductor storage device may correspond to the physicalreading/writing/erasing unit in the nonvolatile semiconductor memory, ormay be different therefrom.

The semiconductor storage device may adopt following data managementunits. The two data management units satisfy the relation that a size ofthe “large unit” is twice or larger natural number times as large as asize of the “small unit”.

(1) A size of the “small unit” is equal to a size of the page unit, anda size of the “large unit” is equal to a size the block unit.

(2) A size of the “small unit” is equal to a size of the page unit, anda size of the “large unit” is equal to a size of the track unit which issmaller than the block unit.

(3) A size of the “small unit” is equal to a size of the cluster unitwhich is smaller than the page unit, and a size of the “large unit” isequal to a size of the block unit.

(4) A size of the “small unit” is equal to a size of the cluster unitwhich is smaller than the page unit, and a size of the “large unit” isequal to a size of the track unit which is smaller than the block unit.

Naturally, the semiconductor storage device may adopt other datamanagement units which satisfy the certain relation described in theabove embodiments, based on the specification (a size of the page unit,or a size of the block unit) of the nonvolatile semiconductor memory, orfile management unit in the host apparatus, for example.

IV. Application Example

Application examples according to the semiconductor storage devicesshown in the above embodiments are described.

Those semiconductor storage devices are applied to, for example, an SSDused as a secondary storage device for a personal computer such as anotebook computer.

FIG. 50 shows a configuration example of the SSD.

The SSD 100 includes plural NAND type flash memories (NAND memories) 10for data storage, a DRAM 101 for data cache or for a work area, a drivecontrol circuit 102 for controlling the NAND memories 10 and the DRAM101, and a power circuit 103.

The first memory area 11 of the above embodiments may be configured inthe DRAM 101. The first memory area 11 configured in the DRAM 101functions as the write cache for the NAND memory 10. The drive controlcircuit 102 may comprise the controller 10 in the above embodiment.

The drive control circuit 102 outputs a control signal for controlling astate display LED provided outside the SSD 100. A FeRAM (Ferro electricRandom Access Memory), a MRAM (Magnetic Random Access Memory), or a NORtype flash memory may be used instead of the DRAM 20. That is, the firstmemory area 11 may be configured in a nonvolatile random access memorywhich has higher writing speed than the NAND memory 10.

The SSD 100 sends and receives data with a host apparatus such as apersonal computer through an ATA interface (ATA I/F), such as a serialATA I/F. The SSD 100 sends and receives data with an equipment for debugthrough an RS232C interface (RS232C I/F).

The power circuit 104 receives the external power source, and generatesplural internal power sources using the external power source. Theseplural internal power sources are supplied to each part in the SSD 100.The power circuit 103 detects the rising of the external source andgenerates a power on reset signal. The power on reset signal is sent tothe drive control circuit 102.

The NAND memory 10 is composed of a plurality of blocks. Each of theblocks is the minimum unit of data erasing. FIG. 51 shows aconfiguration example of one block in the NAND memory 10.

Each block includes (m+1) NAND strings sequentially aligned along the Xdirection (m: integer≧0). In each select transistor ST1 included in the(m+1) NAND strings, the drain is connected to bit lines BL0 to BLm, andthe gate is commonly connected to a select gate line SGD. In a selecttransistor ST2, the source is commonly connected to a source line SL,and the gate is commonly connected to a select gate line SGS.

Each memory cell transistor MT is comprised of an MOSFET (Metal OxideSemiconductor Field Effect Transistor) having a stacked gate structureformed on a semiconductor substrate. The stacked gate structure includesa charge storage layer (floating gate electrode) formed on asemiconductor substrate through a gate insulating film and a controlgate electrode formed on the charge storage layer through an inter-gateinsulation film. The memory cell transistor MT is changed in itsthreshold voltage in accordance with the number of electrons injectedinto a floating gate electrode and stores data in accordance with thedifference in the threshold voltage.

The memory cell transistor MT may be comprised so as to store 1 bit(SLC: Single Level Cell) or 2 or higher bits (MLC: Multi Level Cell).

In each NAND string, the (n+1) memory cell transistors MT are arrangedbetween the source of the selection transistor ST1 and the drain of theselection transistor ST2 so that the respective current pathways areconnected in series. Namely, the plural memory cell transistors MT areconnected in series in the Y direction so that the adjacent memory celltransistors share a diffusion region (source region or drain region).

The control gate electrodes are respectively connected to word lines WL0to WLn in the order from the memory cell transistor MT which is theclosest to the drain side. Thus, the drain of the memory cell transistorMT connected to the word line WL0 is connected to the source of theselection transistor ST1, and the source of the memory cell transistorMT connected to the word line WLn is connected to the drain of theselection transistor ST2.

The word lines WL0 to WLn are connected between the NAND strings in theblock, sharing the control gate electrode in the memory cell transistorMT. Namely, the control gate electrodes in the memory cell transistorMT, which are on the same line in the block, are connected to the sameword line WL. The (m+1) memory cell transistors MT connected to the sameword line WL are treated as the page, and the data writing and the datareading are performed by the page unit.

The bit lines BL0 to BLm are connected between the block, sharing thedrains of the selection transistor ST1. Namely, the NAND strings on thesame line in the plural blocks are connected to the same bit line BL.

The second, third, fourth, and fifth memory areas 12, 13, 14, and 15 ofthe above embodiments may be configured in the NAND memory (memories)10. Each one of the memory areas may be configured over plural NANDmemories 10. Otherwise, each one of the memory areas may be configuredin separate NAND memory 10. Still further, each NAND memory 10 may havea different performance. For example, the fourth memory area 14 may beconfigured in the SLC type NAND memory, and other memory areas may beconfigured in the MLC type NAND memory, and so on.

The plural NAND memories 10 are connected in parallel to the drivecontrol circuit 102. The plural blocks in the NAND memories 10 connectedin parallel may be simultaneously erased and may form the expanded blockunit which is the minimum erasing unit in the SSD 100. The plural pagesin the NAND memories 10 connected in parallel may be simultaneouslywritten and read and may form the expanded page unit which is theminimum writing and reading unit in the SSD 100.

The memory cell transistor MT having a structure with a floating gateelectrode may have a structure which can realize the adjustment of athreshold value by trapping electrons on a nitride film interface as thecharge storage layer, such as an MONOS (Metal Oxide Nitride OxideSilicon) type. Likewise, the memory cell transistor MT having the MONOSstructure may be comprised so as to store 1 bit or 2 or higher bits.

FIG. 52 shows an example of a threshold distribution in a four-levelsystem in which one memory cell stores 2 bits data.

The memory cell stores one of the four-level data “xy” defined by anupper page data “x” and an lower page data “y” in the four-level system.The four-level data is “11”, “01”, “00” and “10”. Data “11” (erasestate) has a state in which the threshold voltage of the memory celltransistor MT is negative.

In the writing operation of the lower page data, data “11” isselectively programmed to data “10” by writing of the lower page data“y”. Before the writing of the upper page data, the thresholddistribution of data “10” is located between the threshold distributionsof data “01” and data “00”, and may be broader than the thresholddistribution obtained after the writing of the upper page data. In thewrite operation of the upper page data, data “11” is selectivelyprogrammed to data “01”, and data “10” is selectively programmed to data“00”, by writing of the upper page data “x”.

The threshold distribution of the memory cell transistors MT is requiredto be finely controlled, when multi-level data storing system isapplied. The threshold distribution is affected a deterioration of thememory cell transistors MT. Therefore, the improvement of the writingefficiency and the decrease of the erasing count are essentiallyeffective, when the nonvolatile semiconductor memories in thesemiconductor storage device adopt the multi-level data storing system.

In addition, as shown in FIG. 52, if the threshold distribution in thestate that only the lower page data is written is different from the onein the state that the upper page data is written, the lower page datapreviously written may be lost caused by the power supply interruptionwhen executing the upper page programming.

Against the above problem, the fourth memory area 14, in which “smallunit” data is written in appending manner, may be composed of thepseudo-SLC blocks. The pseudo-SLC block is a block in which only thelower page is used for the data writing. This configuration prevents theloss of lower page data. Further, the lower page programming does notrequire fine control, the writing speed is improved.

If the fourth memory area 14 is composed of the pseudo-SLC blocks, thepseudo-SLC blocks and the regular blocks (MLC blocks) may interminglewith each other in the second memory area 12. In the four-level system,a storage capacity of the pseudo-SLC block is a half of a storagecapacity of the MLC block. Therefore, at the compaction process in thesecond memory area 12, valid data in the pseudo-SLC blocks is copied tothe MLC block.

FIG. 53 shows a configuration example of the drive control circuit.

The drive control circuit 102 includes a bus 104 for data access, afirst circuit control bus 105, and a second circuit control bus 106.

A processor 107 for controlling the entire drive control circuit 102 isconnected to the first circuit control bus 105. Alternatively, a bootROM 108 storing a boot program in each control program (FW: firmware)therein is connected to the first circuit control bus 105 through a ROMcontroller 109. Further, a clock controller 110 for receiving the poweron reset signal from the power circuit 103 and supplying a reset signaland a clock signal to each section is connected to the first circuitcontrol bus 105.

The second circuit control bus 106 is connected to the first controlcircuit bus 105. A parallel IO (PIO) circuit 111 for supplying a statusdisplay signal to the state display LED and a serial IO (SIO) circuit112 for controlling the RS232C interface are connected to the secondcircuit control bus 106.

An ATA interface controller (ATA controller) 113, a first ECC (ErrorCheck and Correct) circuit 114, a NAND controller 115, and a DRAMcontroller 119 are connected to both the data access bus 104 and thefirst circuit control bus 105. The ATA controller 113 sends and receivesdata with a host apparatus through an ATA interface. An SRAM 102 used asa data work area is connected to the data access bus 104 through an SRAMcontroller 121.

The NAND controller 115 includes a NAND I/F 118 for performing interfaceprocess with the four NAND memories 10, a second ECC circuit 117, and aDMA controller 116 for DMA transfer control for controlling the accessbetween the NAND memory and the DRAM.

FIG. 54 shows a configuration example of a processor.

The processor 107 includes a data control unit 122, and an ATA commandprocessing unit 123, a security control unit 124, a boot loader 125, aninitialization control unit 126, and a debug support unit 127.

The data control unit 122 controls the data transfer between the NANDmemory and the DRAM and various functions with regard to a NAND chipthrough the NAND controller 115 and the first ECC circuit 114.

The ATA command processing unit 123 performs the data transfer processin cooperation with the data control unit 122 through the ATA controller113 and the DRAM controller 119. The security control unit 124 controlsvarious security information in cooperation with the data control unit122 and the ATA command processing unit 123. The boot loader 125 loadseach control program (FW) from the NAND memory 10 to the SRAM 120 whenpowered on.

The initialization control unit 126 initializes each controller andcircuit in the drive control circuit 102. The debug support unit 127processes data for debug which is supplied from the outside through theRS232C interface.

FIG. 55 shows an example of a portable computer with an SSD mountedtherein.

A portable computer 200 includes a main body 201 and a display unit 202.The display unit 202 includes a display housing 203 and a display device204 accommodated in the display housing 203.

The main body 201 includes a chassis 205, a keyboard 206, and a touchpad 207 as a pointing device. The chassis 205 includes a main circuitboard, an ODD unit (Optical Disk Device), a card slot, and the SSD 100.

The card slot is provided so as to be adjacent to the peripheral wall ofthe chassis 205. The peripheral wall has an opening 208 facing the cardslot. A user can insert and remove an additional device into and fromthe card slot from outside the chassis 205 through the opening 208.

The SSD 100 may be used instead of the prior art HDD in the state ofbeing mounted in the portable computer 200 or may be used as anadditional device in the state of being inserted into the card slot ofthe portable computer 200.

FIG. 56 shows an example of a system of a portable computer with an SSDmounted therein.

The portable computer 200 is comprised of CPU 301, a north bridge 302, amain memory 303, a video controller 304, an audio controller 305, asouth bridge 309, BIOS-ROM 310, SSD 100, ODD unit 310, an embeddedcontroller/keyboard controller (EC/KBC) IC 311, and a network controller312.

The CPU 301 is a processor for controlling an operation of the portablecomputer 200, and executes an operating system (OS) loaded from the SSD100 to the main memory 303. The CPU 301 executes these processes, whenthe ODD unit 311 executes one of reading process and writing process toan optical disk.

The CPU 301 executes a system BIOS (Basic Input Output System) stored inBIOS-ROM 310. The system BIOS is a program for controlling a hard wareof the portable computer 200.

The north bridge 302 is a bridge device which connects the local bus ofCPU 301 to the south bridge 309. The north bridge 302 has a memorycontroller for controlling an access to the main memory 303.

The north bridge 302 has a function which executes a communicationbetween the video controller 304 and the audio controller 305 throughthe AGP (Accelerated Graphics Port) bus.

The main memory 303 stores program or data temporary, and functions as awork area of the CPU 301. The main memory 303 is comprised of, forexample, DRAM.

The video controller 304 is a video reproduce controller for controllinga display unit which is used for a display monitor (LCD) 317 of theportable computer 200.

The Audio controller 305 is an audio reproduce controller forcontrolling a speaker 319 of the portable computer 200.

The south bridge 309 controls devices connected to the LPC (Low PinCount) bus, and controls devices connected to the PCI (PeripheralComponent Interconnect) bus. The south bridge 309 controls the SSD 100which is a memory device storing software and data, through the ATAinterface.

The portable computer 200 executes an access to the SSD 100 in thesector unit. The write command, the read command and the flash commandis input through the ATA interface.

The south bridge 309 has a function which controls BIOS-ROM 310 and ODDunit 310.

EC/KBC 311 is one chip microcomputer which is integrated the embeddedcontroller for controlling power supply, and the key board controllerfor controlling the key board (KB) 314 and touch pad 207.

EC/KBC 311 has a function which sets on/off of the power supply of theportable computer 200 based on the operation of the power button byuser. The network controller 312 is, for example, a communication devicewhich executes the communication to the network, for example, theinternet.

Although the semiconductor storage device in the above embodiments iscomprised as an SSD, it can be comprised as, for example, a memory cardtypified by an SD™ card. When the semiconductor storage device iscomprised as the memory card, it can be applied not only to a portablecomputer but also to various electronic devices such as a cell phone, aPDA (Personal Digital Assistant), a digital still camera, and a digitalvideo camera.

The semiconductor storage device of the invention is effective for asecondary storage device for a personal computer such as an SSD and amemory card such as an SD™ card.

What is claimed is:
 1. A semiconductor storage device comprising: aninterface configured to receive data from an external host apparatus; afirst memory configured to store the data by a first unit or less, thefirst unit being an access unit from the external host apparatus; anonvolatile memory configured to store the data transmitted from theinterface via the first memory; and a controller configured to: allocatea plurality of blocks to a first memory area in the nonvolatile memory,each plurality of blocks being a unit of data erasing, the plurality ofblocks allocated to the first memory area including SLC (Single LevelCell) blocks; allocate at least one of the SLC blocks to a second memoryarea in the nonvolatile memory from the first memory area, a pluralityof blocks allocated to the second memory area including SLC blocks andMLC (Multi Level Cell) blocks; store a plurality of data in the firstmemory by the first unit; store data outputted from the first memory inthe SLC block in the first memory area by a first management unit, thefirst management unit being twice or larger natural number times aslarge as the first unit and being less than the unit of data erasing;copy valid data stored in the SLC blocks to one of the MLC blocks when afirst condition is satisfied; and release at least one of the SLC blocksin which no valid data is stored from the second memory area, aftercopying the valid data stored in the SLC blocks.
 2. The semiconductorstorage device according to claim 1, wherein the controller isconfigured to allocate the at least one of the SLC blocks to the secondmemory area from the first memory area when a number of valid datastored in the at least one of the SLC blocks in the first memory area isa first threshold or more.
 3. The semiconductor storage device accordingto claim 2, wherein the controller is configured to copy valid datastored in at least one of the SLC blocks in the first memory area to oneof the MLC blocks when the number of valid data stored in the at leastone of the SLC blocks in the first memory area is less than the firstthreshold.
 4. The semiconductor storage device according to claim 1,wherein the first condition is satisfied when a number of the SLC andMLC blocks allocated to the second memory area exceeds a secondthreshold, and the controller copies valid data stored in the SLC blocksto one of the MLC blocks, within the second memory area, when the firstcondition is satisfied.
 5. The semiconductor storage device according toclaim 1, wherein the SLC blocks include pseudo SLC blocks.
 6. Thesemiconductor storage device according to claim 1, wherein a programmingtime for an SLC block is shorter than that for an MLC block.
 7. Thesemiconductor storage device according to claim 1, wherein a capacity ofan SLC block is smaller than that of an MLC block.
 8. The semiconductorstorage device according to claim 7, wherein the controller isconfigured to invalidate first data, the first data having the samelogical address as data newly stored to the first memory area, stored inthe first or second memory area.
 9. The semiconductor storage deviceaccording to claim 8, wherein the controller is configured to manage theSLC blocks allocated to the first memory area with FIFO (First In FirstOut) data structure sorted by an allocation order.
 10. The semiconductorstorage device according to claim 9, wherein the controller isconfigured to, when storing data to the first memory area, allocate anew SLC block to the first memory area at an input side of the FIFO datastructure.
 11. The semiconductor storage device according to claim 10,wherein the controller is configured to allocate an SLC block having anoldest allocation order at an output side of the FIFO data structure tothe second memory area.
 12. The semiconductor storage device accordingto claim 1, wherein a number of blocks allocatable to the first memoryarea has an upper limit.
 13. The semiconductor storage device accordingto claim 12, wherein the controller is configured to allocate at leastone of the SLC blocks to the second memory area when a number of the SLCblocks allocated to the first memory area exceeds the upper limit. 14.The semiconductor storage device according to claim 1, wherein thenonvolatile memory is a NAND type flash memory.
 15. The semiconductorstorage device according to claim 1, wherein the nonvolatile memoryincludes a plurality of memory chips.
 16. The semiconductor storagedevice according to claim 1, wherein the first memory is a DRAM (DynamicRandom Access Memory).
 17. A method of controlling a semiconductorstorage device, the semiconductor storage device including a nonvolatilememory and a first memory, the method comprising: receiving data from anexternal host apparatus; storing the data by a first unit or less in thefirst memory, the first unit being an access unit from the external hostapparatus; allocating a plurality of blocks to a first memory area inthe nonvolatile memory, each plurality of blocks being a unit of dataerasing, the plurality of blocks allocated to the first memory areaincluding SLC (Single Level Cell) blocks; allocating at least one of theSLC blocks to a second memory area in the nonvolatile memory from thefirst memory area, a plurality of blocks allocated to the second memoryarea including SLC blocks and MLC (Multi Level Cell) blocks; storing thedata in the SLC block in the first memory area by a first managementunit, the data being stored in the first memory, the first managementunit being twice or larger natural number times as large as the firstunit and being less than the unit of data erasing; copying valid datastored in the SLC blocks to one of the MLC blocks when a first conditionis satisfied; and releasing at least one of the SLC blocks in which novalid data is stored from the second memory area, after copying thevalid data stored in the SLC blocks.
 18. The method according to claim17, wherein the allocating the at least one of the SLC blocks to thesecond memory area is executed when a number of valid data stored in theat least one of the SLC blocks in the first memory area is a firstthreshold or more.
 19. The method according to claim 18, wherein thecopying is executed when the number of valid data stored in the at leastone of the SLC blocks in the first memory area is less than the firstthreshold.
 20. The method according to claim 17, wherein the firstcondition is satisfied when a number of the SLC and MLC blocks allocatedto the second memory area exceeds a second threshold, and the copyingincludes copying valid data stored in the SLC blocks to one of the MLCblocks, within the second memory area, when the first condition issatisfied.